diff --git a/source3/auth/auth_builtin.c b/source3/auth/auth_builtin.c
index d61a0ec7bf0..dce58bf8bfc 100644
--- a/source3/auth/auth_builtin.c
+++ b/source3/auth/auth_builtin.c
@@ -103,7 +103,9 @@ static NTSTATUS check_name_to_ntstatus_security(const struct auth_context *auth_
 		return nt_status_string_to_code(user);
 	}
 
-	strlower_m(user);
+	if (!strlower_m(user)) {
+		return NT_STATUS_INVALID_PARAMETER;
+	}
 	error_num = strtoul(user, NULL, 16);
 
 	DEBUG(5,("check_name_to_ntstatus_security: Error for user %s was %lx\n", user, error_num));
diff --git a/source3/auth/auth_util.c b/source3/auth/auth_util.c
index 28d934add37..a08d0945a59 100644
--- a/source3/auth/auth_util.c
+++ b/source3/auth/auth_util.c
@@ -1252,7 +1252,9 @@ static NTSTATUS check_account(TALLOC_CTX *mem_ctx, const char *domain,
 	if (!lower_username) {
 		return NT_STATUS_NO_MEMORY;
 	}
-	strlower_m( lower_username );
+	if (!strlower_m( lower_username )) {
+		return NT_STATUS_INVALID_PARAMETER;
+	}
 
 	orig_dom_user = talloc_asprintf(mem_ctx,
 				"%s%c%s",
diff --git a/source3/auth/pampass.c b/source3/auth/pampass.c
index 87fa8ca9fa3..427c22a8ab2 100644
--- a/source3/auth/pampass.c
+++ b/source3/auth/pampass.c
@@ -249,7 +249,7 @@ static struct chat_struct *make_pw_chat(const char *p)
 
 		special_char_sub(prompt);
 		fstrcpy(t->prompt, prompt);
-		strlower_m(t->prompt);
+		(void)strlower_m(t->prompt);
 		trim_char(t->prompt, ' ', ' ');
 
 		if (!next_token_talloc(frame, &p, &reply, NULL)) {
@@ -262,7 +262,7 @@ static struct chat_struct *make_pw_chat(const char *p)
 
 		special_char_sub(reply);
 		fstrcpy(t->reply, reply);
-		strlower_m(t->reply);
+		(void)strlower_m(t->reply);
 		trim_char(t->reply, ' ', ' ');
 
 	}
diff --git a/source3/auth/pass_check.c b/source3/auth/pass_check.c
index ca992616788..f2d1fc241bc 100644
--- a/source3/auth/pass_check.c
+++ b/source3/auth/pass_check.c
@@ -867,7 +867,9 @@ NTSTATUS pass_check(const struct passwd *pass,
 
 	/* try all lowercase if it's currently all uppercase */
 	if (strhasupper(pass2)) {
-		strlower_m(pass2);
+		if (!strlower_m(pass2)) {
+			return NT_STATUS_INVALID_PARAMETER;
+		}
 		nt_status = password_check(pass2, (const void *)rhost);
 		if (NT_STATUS_IS_OK(nt_status)) {
 			return (nt_status);
@@ -880,7 +882,9 @@ NTSTATUS pass_check(const struct passwd *pass,
 	}
 
 	/* last chance - all combinations of up to level chars upper! */
-	strlower_m(pass2);
+	if (!strlower_m(pass2)) {
+		return NT_STATUS_INVALID_PARAMETER;
+	}
 
 	nt_status = string_combinations(pass2, password_check, level,
 					(const void *)rhost);
diff --git a/source3/auth/user_util.c b/source3/auth/user_util.c
index 8938aeb003a..4842192051e 100644
--- a/source3/auth/user_util.c
+++ b/source3/auth/user_util.c
@@ -164,7 +164,9 @@ bool user_in_netgroup(TALLOC_CTX *ctx, const char *user, const char *ngname)
 	if (!lowercase_user) {
 		return false;
 	}
-	strlower_m(lowercase_user);
+	if (!strlower_m(lowercase_user)) {
+		return false;
+	}
 
 	if (strcmp(user,lowercase_user) == 0) {
 		/* user name was already lower case! */
diff --git a/source3/client/client.c b/source3/client/client.c
index 28fc30aeb44..2c949ac4760 100644
--- a/source3/client/client.c
+++ b/source3/client/client.c
@@ -1086,7 +1086,10 @@ static int do_get(const char *rname, const char *lname_in, bool reget)
 	}
 
 	if (lowercase) {
-		strlower_m(lname);
+		if (!strlower_m(lname)) {
+			d_printf("strlower_m %s failed\n", lname);
+			return 1;
+		}
 	}
 
 	status = cli_resolve_path(ctx, "", auth_info, cli, rname, &targetcli,
@@ -1296,7 +1299,9 @@ static NTSTATUS do_mget(struct cli_state *cli_state, struct file_info *finfo,
 
 	string_replace(finfo->name,'\\','/');
 	if (lowercase) {
-		strlower_m(finfo->name);
+		if (!strlower_m(finfo->name)) {
+			return NT_STATUS_INVALID_PARAMETER;
+		}
 	}
 
 	if (!directory_exist(finfo->name) &&
diff --git a/source3/client/clitar.c b/source3/client/clitar.c
index c0b6e4e7f19..cae512b5e9b 100644
--- a/source3/client/clitar.c
+++ b/source3/client/clitar.c
@@ -173,7 +173,7 @@ static void writetarheader(int f, const char *aname, uint64_t size, time_t mtime
 	fixtarname(hb.dbuf.name, aname, (l+2 >= NAMSIZ) ? NAMSIZ : l + 2);
 
 	if (lowercase)
-		strlower_m(hb.dbuf.name);
+		(void)strlower_m(hb.dbuf.name);
 
 	/* write out a "standard" tar format header */
 
diff --git a/source3/lib/afs.c b/source3/lib/afs.c
index 849e9ce55d1..4b6e6ecaf36 100644
--- a/source3/lib/afs.c
+++ b/source3/lib/afs.c
@@ -259,7 +259,9 @@ bool afs_login(connection_struct *conn)
 
 	/* The pts command always generates completely lower-case user
 	 * names. */
-	strlower_m(afs_username);
+	if (!strlower_m(afs_username)) {
+		return false;
+	}
 
 	cell = strchr(afs_username, '@');
 
diff --git a/source3/lib/substitute.c b/source3/lib/substitute.c
index 44582860a19..a254bcaa7d5 100644
--- a/source3/lib/substitute.c
+++ b/source3/lib/substitute.c
@@ -66,7 +66,10 @@ bool set_local_machine_name(const char *local_name, bool perm)
 	/* alpha_strcpy includes the space for the terminating nul. */
 	alpha_strcpy(local_machine,tmp_local_machine,
 			SAFE_NETBIOS_CHARS,len+1);
-	strlower_m(local_machine);
+	if (!strlower_m(local_machine)) {
+		TALLOC_FREE(tmp_local_machine);
+		return false;
+	}
 	TALLOC_FREE(tmp_local_machine);
 
 	already_perm = perm;
@@ -118,7 +121,10 @@ bool set_remote_machine_name(const char *remote_name, bool perm)
 	/* alpha_strcpy includes the space for the terminating nul. */
 	alpha_strcpy(remote_machine,tmp_remote_machine,
 			SAFE_NETBIOS_CHARS,len+1);
-	strlower_m(remote_machine);
+	if (!strlower_m(remote_machine)) {
+		TALLOC_FREE(tmp_remote_machine);
+		return false;
+	}
 	TALLOC_FREE(tmp_remote_machine);
 
 	already_perm = perm;
@@ -153,7 +159,10 @@ void sub_set_smb_name(const char *name)
 		return;
 	}
 	trim_char(tmp, ' ', ' ');
-	strlower_m(tmp);
+	if (!strlower_m(tmp)) {
+		TALLOC_FREE(tmp);
+		return;
+	}
 
 	len = strlen(tmp);
 
diff --git a/source3/lib/username.c b/source3/lib/username.c
index 7435a59ac7a..665fbb42536 100644
--- a/source3/lib/username.c
+++ b/source3/lib/username.c
@@ -112,7 +112,11 @@ static struct passwd *Get_Pwnam_internals(TALLOC_CTX *mem_ctx,
 
 	/* Try in all lower case first as this is the most 
 	   common case on UNIX systems */
-	strlower_m(user2);
+	if (!strlower_m(user2)) {
+		DEBUG(5,("strlower_m %s failed\n", user2));
+		goto done;
+	}
+
 	DEBUG(5,("Trying _Get_Pwnam(), username as lowercase is %s\n",user2));
 	ret = getpwnam_alloc_cached(mem_ctx, user2);
 	if(ret)
@@ -141,7 +145,10 @@ static struct passwd *Get_Pwnam_internals(TALLOC_CTX *mem_ctx,
 	}
 
 	/* Try all combinations up to usernamelevel */
-	strlower_m(user2);
+	if (!strlower_m(user2)) {
+		DEBUG(5,("strlower_m %s failed\n", user2));
+		goto done;
+	}
 	DEBUG(5,("Checking combinations of %d uppercase letters in %s\n",
 		 lp_usernamelevel(), user2));
 	ret = uname_string_combinations(user2, mem_ctx, getpwnam_alloc_cached,
diff --git a/source3/lib/util.c b/source3/lib/util.c
index 9c380c5a02d..b8513f6b9fa 100644
--- a/source3/lib/util.c
+++ b/source3/lib/util.c
@@ -1892,8 +1892,14 @@ bool unix_wild_match(const char *pattern, const char *string)
 		TALLOC_FREE(ctx);
 		return false;
 	}
-	strlower_m(p2);
-	strlower_m(s2);
+	if (!strlower_m(p2)) {
+		TALLOC_FREE(ctx);
+		return false;
+	}
+	if (!strlower_m(s2)) {
+		TALLOC_FREE(ctx);
+		return false;
+	}
 
 	/* Remove any *? and ** from the pattern as they are meaningless */
 	for(p = p2; *p; p++) {
diff --git a/source3/lib/util_str.c b/source3/lib/util_str.c
index 8962b23da0d..c302851335c 100644
--- a/source3/lib/util_str.c
+++ b/source3/lib/util_str.c
@@ -60,8 +60,7 @@ bool strnorm(char *s, int case_default)
 	if (case_default == CASE_UPPER)
 		return strupper_m(s);
 	else
-		strlower_m(s);
-	return true; /* FIXME - return strlower_m value later. */
+		return strlower_m(s);
 }
 
 /**
@@ -491,7 +490,6 @@ bool strlower_m(char *s)
 	/* Catch mb conversion errors that may not terminate. */
 	if (errno) {
 		s[len-1] = '\0';
-		ret = false;
 	}
 	errno = errno_save;
 	return ret;
@@ -1033,7 +1031,10 @@ char *talloc_asprintf_strlower_m(TALLOC_CTX *t, const char *fmt, ...)
 	if (ret == NULL) {
 		return NULL;
 	}
-	strlower_m(ret);
+	if (!strlower_m(ret)) {
+		TALLOC_FREE(ret);
+		return NULL;
+	}
 	return ret;
 }
 
diff --git a/source3/libads/ads_struct.c b/source3/libads/ads_struct.c
index 285057ba53d..45d00a39a3a 100644
--- a/source3/libads/ads_struct.c
+++ b/source3/libads/ads_struct.c
@@ -108,7 +108,11 @@ char *ads_build_domain(const char *dn)
 		return NULL;		
 	}	
 
-	strlower_m( dnsdomain );	
+	if (!strlower_m( dnsdomain )) {
+		SAFE_FREE(dnsdomain);
+		return NULL;
+	}
+
 	all_string_sub( dnsdomain, "dc=", "", 0);
 	all_string_sub( dnsdomain, ",", ".", 0 );
 
diff --git a/source3/libads/kerberos.c b/source3/libads/kerberos.c
index 80f99de4823..1093d12c2c6 100644
--- a/source3/libads/kerberos.c
+++ b/source3/libads/kerberos.c
@@ -356,7 +356,7 @@ char* kerberos_standard_des_salt( void )
 	fstring salt;
 
 	fstr_sprintf( salt, "host/%s.%s@", lp_netbios_name(), lp_realm() );
-	strlower_m( salt );
+	(void)strlower_m( salt );
 	fstrcat( salt, lp_realm() );
 
 	return SMB_STRDUP( salt );
diff --git a/source3/libads/ldap.c b/source3/libads/ldap.c
index fa88244598b..946c1a36a72 100644
--- a/source3/libads/ldap.c
+++ b/source3/libads/ldap.c
@@ -1954,7 +1954,10 @@ ADS_STATUS ads_add_service_principal_name(ADS_STRUCT *ads, const char *machine_n
 		goto out;
 	}
 
-	strlower_m(&psp1[strlen(spn)]);
+	if (!strlower_m(&psp1[strlen(spn)])) {
+		ret = ADS_ERROR(LDAP_NO_MEMORY);
+		goto out;
+	}
 	servicePrincipalName[0] = psp1;
 
 	DEBUG(5,("ads_add_service_principal_name: INFO: Adding %s to host %s\n", 
@@ -1972,7 +1975,10 @@ ADS_STATUS ads_add_service_principal_name(ADS_STRUCT *ads, const char *machine_n
 		goto out;
 	}
 
-	strlower_m(&psp2[strlen(spn)]);
+	if (!strlower_m(&psp2[strlen(spn)])) {
+		ret = ADS_ERROR(LDAP_NO_MEMORY);
+		goto out;
+	}
 	servicePrincipalName[1] = psp2;
 
 	DEBUG(5,("ads_add_service_principal_name: INFO: Adding %s to host %s\n", 
@@ -3468,7 +3474,10 @@ ADS_STATUS ads_leave_realm(ADS_STRUCT *ads, const char *hostname)
 
 	/* hostname must be lowercase */
 	host = SMB_STRDUP(hostname);
-	strlower_m(host);
+	if (!strlower_m(host)) {
+		SAFE_FREE(host);
+		return ADS_ERROR_SYSTEM(EINVAL);
+	}
 
 	status = ads_find_machine_acct(ads, &res, host);
 	if (!ADS_ERR_OK(status)) {
diff --git a/source3/libads/sasl.c b/source3/libads/sasl.c
index a04ac9dd691..438db05df89 100644
--- a/source3/libads/sasl.c
+++ b/source3/libads/sasl.c
@@ -652,7 +652,12 @@ static ADS_STATUS ads_guess_service_principal(ADS_STRUCT *ads,
 			return ADS_ERROR(LDAP_NO_MEMORY);
 		}
 
-		strlower_m(server);
+		if (!strlower_m(server)) {
+			SAFE_FREE(server);
+			SAFE_FREE(server_realm);
+			return ADS_ERROR(LDAP_NO_MEMORY);
+		}
+
 		if (!strupper_m(server_realm)) {
 			SAFE_FREE(server);
 			SAFE_FREE(server_realm);
@@ -683,7 +688,12 @@ static ADS_STATUS ads_guess_service_principal(ADS_STRUCT *ads,
 			return ADS_ERROR(LDAP_NO_MEMORY);
 		}
 
-		strlower_m(server);
+		if (!strlower_m(server)) {
+			SAFE_FREE(server);
+			SAFE_FREE(server_realm);
+			return ADS_ERROR(LDAP_NO_MEMORY);
+		}
+
 		if (!strupper_m(server_realm)) {
 			SAFE_FREE(server);
 			SAFE_FREE(server_realm);
diff --git a/source3/libnet/libnet_join.c b/source3/libnet/libnet_join.c
index 5806f7bc75c..d6aa7937ee5 100644
--- a/source3/libnet/libnet_join.c
+++ b/source3/libnet/libnet_join.c
@@ -395,7 +395,9 @@ static ADS_STATUS libnet_join_set_machine_spn(TALLOC_CTX *mem_ctx,
 			     r->out.dns_domain_name);
 	}
 
-	strlower_m(my_fqdn);
+	if (!strlower_m(my_fqdn)) {
+		return ADS_ERROR_LDAP(LDAP_NO_MEMORY);
+	}
 
 	if (!strequal(my_fqdn, r->in.machine_name)) {
 		spn = talloc_asprintf(mem_ctx, "HOST/%s", my_fqdn);
@@ -817,7 +819,9 @@ static NTSTATUS libnet_join_joindomain_rpc_unsecure(TALLOC_CTX *mem_ctx,
 
 	/* according to WKSSVC_JOIN_FLAGS_MACHINE_PWD_PASSED */
 	fstrcpy(trust_passwd, r->in.admin_password);
-	strlower_m(trust_passwd);
+	if (!strlower_m(trust_passwd)) {
+		return NT_STATUS_INVALID_PARAMETER;
+	}
 
 	/*
 	 * Machine names can be 15 characters, but the max length on
@@ -934,7 +938,10 @@ static NTSTATUS libnet_join_joindomain_rpc(TALLOC_CTX *mem_ctx,
 	/* Create domain user */
 
 	acct_name = talloc_asprintf(mem_ctx, "%s$", r->in.machine_name);
-	strlower_m(acct_name);
+	if (!strlower_m(acct_name)) {
+		status = NT_STATUS_INVALID_PARAMETER;
+		goto done;
+	}
 
 	init_lsa_String(&lsa_acct_name, acct_name);
 
@@ -1367,7 +1374,10 @@ static NTSTATUS libnet_join_unjoindomain_rpc(TALLOC_CTX *mem_ctx,
 	/* Create domain user */
 
 	acct_name = talloc_asprintf(mem_ctx, "%s$", r->in.machine_name);
-	strlower_m(acct_name);
+	if (!strlower_m(acct_name)) {
+		status = NT_STATUS_INVALID_PARAMETER;
+		goto done;
+	}
 
 	init_lsa_String(&lsa_acct_name, acct_name);
 
diff --git a/source3/librpc/crypto/gse_krb5.c b/source3/librpc/crypto/gse_krb5.c
index dbcc520048d..43f545ad4cd 100644
--- a/source3/librpc/crypto/gse_krb5.c
+++ b/source3/librpc/crypto/gse_krb5.c
@@ -96,7 +96,10 @@ static krb5_error_code get_host_principal(krb5_context krbctx,
 		return -1;
 	}
 
-	strlower_m(host_princ_s);
+	if (!strlower_m(host_princ_s)) {
+		SAFE_FREE(host_princ_s);
+		return -1;
+	}
 	ret = smb_krb5_parse_name(krbctx, host_princ_s, host_princ);
 	if (ret) {
 		DEBUG(1, (__location__ ": smb_krb5_parse_name(%s) "
diff --git a/source3/modules/vfs_afsacl.c b/source3/modules/vfs_afsacl.c
index ab7ef30e6b2..770f6a33f01 100644
--- a/source3/modules/vfs_afsacl.c
+++ b/source3/modules/vfs_afsacl.c
@@ -804,7 +804,9 @@ static bool nt_to_afs_acl(const char *filename,
 				if (tmp == NULL) {
 					return false;
 				}
-				strlower_m(tmp);
+				if (!strlower_m(tmp)) {
+					return false;
+				}
 				name = tmp;
 			}
 
diff --git a/source3/param/loadparm.c b/source3/param/loadparm.c
index d4ee8a22f2b..5dcb92628cb 100644
--- a/source3/param/loadparm.c
+++ b/source3/param/loadparm.c
@@ -1653,7 +1653,10 @@ char *canonicalize_servicename(TALLOC_CTX *ctx, const char *src)
 	result = talloc_strdup(ctx, src);
 	SMB_ASSERT(result != NULL);
 
-	strlower_m(result);
+	if (!strlower_m(result)) {
+		TALLOC_FREE(result);
+		return NULL;
+	}
 	return result;
 }
 
diff --git a/source3/param/service.c b/source3/param/service.c
index 5f0910fe0ad..85047a8e082 100644
--- a/source3/param/service.c
+++ b/source3/param/service.c
@@ -191,7 +191,9 @@ int find_service(TALLOC_CTX *ctx, const char *service_in, char **p_service_out)
 	/* Is it a usershare service ? */
 	if (iService < 0 && *lp_usershare_path(talloc_tos())) {
 		/* Ensure the name is canonicalized. */
-		strlower_m(*p_service_out);
+		if (!strlower_m(*p_service_out)) {
+			goto fail;
+		}
 		iService = load_usershare_service(*p_service_out);
 	}
 
diff --git a/source3/passdb/pdb_interface.c b/source3/passdb/pdb_interface.c
index 7a73fbfacf0..cdbb378e947 100644
--- a/source3/passdb/pdb_interface.c
+++ b/source3/passdb/pdb_interface.c
@@ -472,7 +472,9 @@ static NTSTATUS pdb_default_create_user(struct pdb_methods *methods,
 		/* lowercase the username before creating the Unix account for 
 		   compatibility with previous Samba releases */
 		fstrcpy( name2, name );
-		strlower_m( name2 );
+		if (!strlower_m( name2 )) {
+			return NT_STATUS_INVALID_PARAMETER;
+		}
 		add_script = talloc_all_string_sub(tmp_ctx,
 					add_script,
 					"%u",
@@ -598,7 +600,9 @@ static NTSTATUS pdb_default_delete_user(struct pdb_methods *methods,
 	   external scripts */
 
 	fstrcpy( username, pdb_get_username(sam_acct) );
-	strlower_m( username );
+	if (!strlower_m( username )) {
+		return status;
+	}
 
 	smb_delete_user( username );
 
diff --git a/source3/passdb/pdb_ipa.c b/source3/passdb/pdb_ipa.c
index bbd3339f2f9..c0eb48d4489 100644
--- a/source3/passdb/pdb_ipa.c
+++ b/source3/passdb/pdb_ipa.c
@@ -787,7 +787,9 @@ static struct pdb_domain_info *pdb_ipasam_get_domain_info(struct pdb_methods *pd
 	if (info->dns_domain == NULL) {
 		goto fail;
 	}
-	strlower_m(info->dns_domain);
+	if (!strlower_m(info->dns_domain)) {
+		goto fail;
+	}
 	info->dns_forest = talloc_strdup(info, info->dns_domain);
 
 	/* we expect a domain SID to have 4 sub IDs */
diff --git a/source3/passdb/pdb_ldap.c b/source3/passdb/pdb_ldap.c
index 56225a2965d..9b4d8a6a4dd 100644
--- a/source3/passdb/pdb_ldap.c
+++ b/source3/passdb/pdb_ldap.c
@@ -2015,9 +2015,14 @@ static NTSTATUS ldapsam_rename_sam_account(struct pdb_methods *my_methods,
 	   posix name but preserve the case in passdb */
 
 	fstrcpy( oldname_lower, oldname );
-	strlower_m( oldname_lower );
+	if (!strlower_m( oldname_lower )) {
+		return NT_STATUS_INVALID_PARAMETER;
+	}
 	fstrcpy( newname_lower, newname );
-	strlower_m( newname_lower );
+	if (!strlower_m( newname_lower )) {
+		return NT_STATUS_INVALID_PARAMETER;
+	}
+
 	rename_script = realloc_string_sub2(rename_script,
 					"%unew",
 					newname_lower,
diff --git a/source3/passdb/pdb_tdb.c b/source3/passdb/pdb_tdb.c
index 12958623036..bd6e123e31c 100644
--- a/source3/passdb/pdb_tdb.c
+++ b/source3/passdb/pdb_tdb.c
@@ -572,7 +572,9 @@ static NTSTATUS tdbsam_getsampwnam (struct pdb_methods *my_methods,
 
 	/* Data is stored in all lower-case */
 	fstrcpy(name, sname);
-	strlower_m(name);
+	if (!strlower_m(name)) {
+		return NT_STATUS_INVALID_PARAMETER;
+	}
 
 	/* set search key */
 	slprintf(keystr, sizeof(keystr)-1, "%s%s", USERPREFIX, name);
@@ -668,7 +670,9 @@ static bool tdb_delete_samacct_only( struct samu *sam_pass )
 	NTSTATUS status;
 
 	fstrcpy(name, pdb_get_username(sam_pass));
-	strlower_m(name);
+	if (!strlower_m(name)) {
+		return false;
+	}
 
   	/* set the search key */
 
@@ -712,7 +716,9 @@ static NTSTATUS tdbsam_delete_sam_account(struct pdb_methods *my_methods,
 	}
 
 	fstrcpy(name, pdb_get_username(sam_pass));
-	strlower_m(name);
+	if (!strlower_m(name)) {
+		return NT_STATUS_INVALID_PARAMETER;
+	}
 
   	/* set the search key */
 
@@ -785,7 +791,9 @@ static bool tdb_update_samacct_only( struct samu* newpwd, int flag )
 	data.dptr = buf;
 
 	fstrcpy(name, pdb_get_username(newpwd));
-	strlower_m(name);
+	if (!strlower_m(name)) {
+		goto done;
+	}
 
 	DEBUG(5, ("Storing %saccount %s with RID %d\n",
 		  flag == TDB_INSERT ? "(new) " : "", name,
@@ -823,7 +831,9 @@ static bool tdb_update_ridrec_only( struct samu* newpwd, int flag )
 	NTSTATUS status;
 
 	fstrcpy(name, pdb_get_username(newpwd));
-	strlower_m(name);
+	if (!strlower_m(name)) {
+		return false;
+	}
 
 	/* setup RID data */
 	data = string_term_tdb_data(name);
@@ -1032,10 +1042,14 @@ static NTSTATUS tdbsam_rename_sam_account(struct pdb_methods *my_methods,
 	   so that we lower case the posix name but preserve the case in passdb */
 
 	fstrcpy( oldname_lower, pdb_get_username(old_acct) );
-	strlower_m( oldname_lower );
+	if (!strlower_m( oldname_lower )) {
+		goto cancel;
+	}
 
 	fstrcpy( newname_lower, newname );
-	strlower_m( newname_lower );
+	if (!strlower_m( newname_lower )) {
+		goto cancel;
+	}
 
 	rename_script = talloc_string_sub2(new_acct,
 				rename_script,
diff --git a/source3/printing/lpq_parse.c b/source3/printing/lpq_parse.c
index 21e7b37faf0..91fc2ead712 100644
--- a/source3/printing/lpq_parse.c
+++ b/source3/printing/lpq_parse.c
@@ -1117,7 +1117,9 @@ bool parse_lpq_entry(enum printing_types printing_type,char *line,
 			printer status line: 
 			handle them so that most severe condition is shown */
 		int i;
-		strlower_m(line);
+		if (!strlower_m(line)) {
+			return false;
+		}
       
 		switch (status->status) {
 			case LPSTAT_OK:
diff --git a/source3/printing/nt_printing_tdb.c b/source3/printing/nt_printing_tdb.c
index 028dc0b1da9..870231af8c0 100644
--- a/source3/printing/nt_printing_tdb.c
+++ b/source3/printing/nt_printing_tdb.c
@@ -54,7 +54,7 @@ static TDB_DATA make_printer_tdbkey(TALLOC_CTX *ctx, const char *sharename )
 	TDB_DATA key;
 
 	fstrcpy(share, sharename);
-	strlower_m(share);
+	(void)strlower_m(share);
 
 	keystr = talloc_asprintf(ctx, "%s%s", PRINTERS_PREFIX, share);
 	key = string_term_tdb_data(keystr ? keystr : "");
@@ -74,7 +74,7 @@ static TDB_DATA make_printers_secdesc_tdbkey(TALLOC_CTX *ctx,
 	TDB_DATA key;
 
 	fstrcpy(share, sharename );
-	strlower_m(share);
+	(void)strlower_m(share);
 
 	keystr = talloc_asprintf(ctx, "%s%s", SECDESC_PREFIX, share);
 	key = string_term_tdb_data(keystr ? keystr : "");
diff --git a/source3/rpc_server/dfs/srv_dfs_nt.c b/source3/rpc_server/dfs/srv_dfs_nt.c
index 49e65066e5f..fc9c92b5522 100644
--- a/source3/rpc_server/dfs/srv_dfs_nt.c
+++ b/source3/rpc_server/dfs/srv_dfs_nt.c
@@ -138,7 +138,9 @@ WERROR _dfs_Remove(struct pipes_struct *p, struct dfs_Remove *r)
 		if (!altpath) {
 			return WERR_NOMEM;
 		}
-		strlower_m(altpath);
+		if (!strlower_m(altpath)) {
+			return WERR_INVALID_PARAM;
+		}
 		DEBUG(5,("init_reply_dfs_remove: Request to remove %s -> %s\\%s.\n",
 			r->in.dfs_entry_path, r->in.servername, r->in.sharename));
 	}
diff --git a/source3/rpc_server/dssetup/srv_dssetup_nt.c b/source3/rpc_server/dssetup/srv_dssetup_nt.c
index fef2dbd7e03..1a3998b8bef 100644
--- a/source3/rpc_server/dssetup/srv_dssetup_nt.c
+++ b/source3/rpc_server/dssetup/srv_dssetup_nt.c
@@ -78,7 +78,9 @@ static WERROR fill_dsrole_dominfo_basic(TALLOC_CTX *ctx,
 		if (!dnsdomain) {
 			return WERR_NOMEM;
 		}
-		strlower_m(dnsdomain);
+		if (!strlower_m(dnsdomain)) {
+			return WERR_INVALID_PARAM;
+		}
 		basic->dns_domain = dnsdomain;
 
 		/* FIXME!! We really should fill in the correct forest
diff --git a/source3/smbd/negprot.c b/source3/smbd/negprot.c
index c9350afa494..e33350c932b 100644
--- a/source3/smbd/negprot.c
+++ b/source3/smbd/negprot.c
@@ -206,7 +206,7 @@ DATA_BLOB negprot_spnego(TALLOC_CTX *ctx, struct smbd_server_connection *sconn)
 	memset(blob_out.data, '\0', 16);
 
 	checked_strlcpy(unix_name, lp_netbios_name(), sizeof(unix_name));
-	strlower_m(unix_name);
+	(void)strlower_m(unix_name);
 	push_ascii_nstring(dos_name, unix_name);
 	strlcpy((char *)blob_out.data, dos_name, 17);
 
diff --git a/source3/smbd/service.c b/source3/smbd/service.c
index ce9cff90e24..0cd48f89504 100644
--- a/source3/smbd/service.c
+++ b/source3/smbd/service.c
@@ -1098,7 +1098,11 @@ connection_struct *make_connection(struct smbd_server_connection *sconn,
 		return NULL;
 	}
 
-	strlower_m(service);
+	if (!strlower_m(service)) {
+		DEBUG(2, ("strlower_m %s failed\n", service));
+		*status = NT_STATUS_INVALID_PARAMETER;
+		return NULL;
+	}
 
 	snum = find_service(talloc_tos(), service, &service);
 	if (!service) {
diff --git a/source3/smbd/smb2_tcon.c b/source3/smbd/smb2_tcon.c
index 2cf91af3ff5..1346d1309be 100644
--- a/source3/smbd/smb2_tcon.c
+++ b/source3/smbd/smb2_tcon.c
@@ -202,7 +202,10 @@ static NTSTATUS smbd_smb2_tree_connect(struct smbd_smb2_request *req,
 		return NT_STATUS_NO_MEMORY;
 	}
 
-	strlower_m(service);
+	if (!strlower_m(service)) {
+		DEBUG(2, ("strlower_m %s failed\n", service));
+		return NT_STATUS_INVALID_PARAMETER;
+	}
 
 	/* TODO: do more things... */
 	if (strequal(service,HOMES_NAME)) {
diff --git a/source3/torture/masktest.c b/source3/torture/masktest.c
index 74f33a5cddc..58e09822a14 100644
--- a/source3/torture/masktest.c
+++ b/source3/torture/masktest.c
@@ -269,12 +269,12 @@ static NTSTATUS listfn(const char *mnt, struct file_info *f, const char *s,
 
 
 	fstrcpy(state->short_name, f->short_name ? f->short_name : "");
-	strlower_m(state->short_name);
+	(void)strlower_m(state->short_name);
 	*state->pp_long_name = SMB_STRDUP(f->name);
 	if (!*state->pp_long_name) {
 		return NT_STATUS_NO_MEMORY;
 	}
-	strlower_m(*state->pp_long_name);
+	(void)strlower_m(*state->pp_long_name);
 	return NT_STATUS_OK;
 }
 
diff --git a/source3/utils/net_ads.c b/source3/utils/net_ads.c
index b1eac52df2c..b1d55f10b03 100644
--- a/source3/utils/net_ads.c
+++ b/source3/utils/net_ads.c
@@ -1256,7 +1256,9 @@ static NTSTATUS net_update_dns_ext(TALLOC_CTX *mem_ctx, ADS_STRUCT *ads,
 	} else {
 		name_to_fqdn( machine_name, lp_netbios_name() );
 	}
-	strlower_m( machine_name );
+	if (!strlower_m( machine_name )) {
+		return NT_STATUS_INVALID_PARAMETER;
+	}
 
 	if (num_addrs == 0 || iplist == NULL) {
 		/*
@@ -2192,7 +2194,11 @@ int net_ads_changetrustpw(struct net_context *c, int argc, const char **argv)
 	}
 
 	fstrcpy(my_name, lp_netbios_name());
-	strlower_m(my_name);
+	if (!strlower_m(my_name)) {
+		ads_destroy(&ads);
+		return -1;
+	}
+
 	if (asprintf(&host_principal, "%s$@%s", my_name, ads->config.realm) == -1) {
 		ads_destroy(&ads);
 		return -1;
diff --git a/source3/utils/net_rpc_join.c b/source3/utils/net_rpc_join.c
index 50383fee6b5..ed81aacac79 100644
--- a/source3/utils/net_rpc_join.c
+++ b/source3/utils/net_rpc_join.c
@@ -321,7 +321,10 @@ int net_rpc_join_newstyle(struct net_context *c, int argc, const char **argv)
 		status = NT_STATUS_NO_MEMORY;
 		goto done;
 	}
-	strlower_m(acct_name);
+	if (!strlower_m(acct_name)) {
+		status = NT_STATUS_INVALID_PARAMETER;
+		goto done;
+	}
 
 	init_lsa_String(&lsa_acct_name, acct_name);
 
diff --git a/source3/utils/net_usershare.c b/source3/utils/net_usershare.c
index 153b45e7f85..382fe2f250c 100644
--- a/source3/utils/net_usershare.c
+++ b/source3/utils/net_usershare.c
@@ -523,7 +523,9 @@ static int net_usershare_info(struct net_context *c, int argc, const char **argv
 			return net_usershare_info_usage(c, argc, argv);
 	}
 
-	strlower_m(wcard);
+	if (!strlower_m(wcard)) {
+		return -1;
+	}
 
 	ctx = talloc_init("share_info");
 	ret = get_share_list(ctx, wcard, only_ours);
@@ -1036,7 +1038,9 @@ static int net_usershare_list(struct net_context *c, int argc,
 			return net_usershare_list_usage(c, argc, argv);
 	}
 
-	strlower_m(wcard);
+	if (!strlower_m(wcard)) {
+		return -1;
+	}
 
 	ctx = talloc_init("share_list");
 	ret = get_share_list(ctx, wcard, only_ours);
diff --git a/source3/utils/pdbedit.c b/source3/utils/pdbedit.c
index 06eed201f4e..8a3551bf6bb 100644
--- a/source3/utils/pdbedit.c
+++ b/source3/utils/pdbedit.c
@@ -655,7 +655,11 @@ static int set_machine_info(const char *machinename,
 		return -1;
 	}
 
-	strlower_m(name);
+	if (!strlower_m(name)) {
+		fprintf(stderr, "strlower_m %s failed\n", name);
+		TALLOC_FREE(sam_pwent);
+		return -1;
+	}
 
 	ret = pdb_getsampwnam(sam_pwent, name);
 	if (!ret) {
@@ -853,7 +857,10 @@ static int new_machine(const char *machinename, char *machine_sid)
 		return -1;
 	}
 
-	strlower_m(name);
+	if (!strlower_m(name)) {
+		fprintf(stderr, "strlower_m %s failed\n", name);
+		return -1;
+	}
 
 	flags = LOCAL_ADD_USER | LOCAL_TRUST_ACCOUNT | LOCAL_SET_PASSWORD;
 
diff --git a/source3/utils/smbpasswd.c b/source3/utils/smbpasswd.c
index f845147da48..66c80da618e 100644
--- a/source3/utils/smbpasswd.c
+++ b/source3/utils/smbpasswd.c
@@ -370,7 +370,11 @@ static int process_root(int local_flags)
 		if (local_flags & LOCAL_ADD_USER) {
 		        SAFE_FREE(new_passwd);
 			new_passwd = smb_xstrdup(user_name);
-			strlower_m(new_passwd);
+			if (!strlower_m(new_passwd)) {
+				fprintf(stderr, "strlower_m %s failed\n",
+					new_passwd);
+				exit(1);
+			}
 		}
 
 		/*
diff --git a/source3/winbindd/wb_fill_pwent.c b/source3/winbindd/wb_fill_pwent.c
index a716245ce85..62b1b4a1896 100644
--- a/source3/winbindd/wb_fill_pwent.c
+++ b/source3/winbindd/wb_fill_pwent.c
@@ -111,7 +111,10 @@ static void wb_fill_pwent_sid2gid_done(struct tevent_req *subreq)
 	/* Username */
 
 	fstrcpy(user_name, state->info->acct_name);
-	strlower_m(user_name);
+	if (!strlower_m(user_name)) {
+		tevent_req_nterror(req, NT_STATUS_INVALID_PARAMETER);
+		return;
+	}
 	status = normalize_name_map(state, domain, user_name, &mapped_name);
 
 	/* Basic removal of whitespace */
diff --git a/source3/winbindd/winbindd_cache.c b/source3/winbindd/winbindd_cache.c
index cfa843424a3..2c9dd4a9b3e 100644
--- a/source3/winbindd/winbindd_cache.c
+++ b/source3/winbindd/winbindd_cache.c
@@ -1868,7 +1868,7 @@ static NTSTATUS name_to_sid(struct winbindd_domain *domain,
 			if (!strupper_m(discard_const_p(char, domain_name))) {
 				return NT_STATUS_INVALID_PARAMETER;
 			}
-			strlower_m(discard_const_p(char, name));
+			(void)strlower_m(discard_const_p(char, name));
 			wcache_save_sid_to_name(domain, status, sid, domain_name, name, *type);
 		}
 	}
diff --git a/source3/winbindd/winbindd_pam.c b/source3/winbindd/winbindd_pam.c
index 48bb79bdcdb..d8febe6a5c4 100644
--- a/source3/winbindd/winbindd_pam.c
+++ b/source3/winbindd/winbindd_pam.c
@@ -217,7 +217,9 @@ static NTSTATUS append_afs_token(TALLOC_CTX *mem_ctx,
 		return NT_STATUS_NO_MEMORY;
 	}
 
-	strlower_m(afsname);
+	if (!strlower_m(afsname)) {
+		return NT_STATUS_INVALID_PARAMETER;
+	}
 
 	DEBUG(10, ("Generating token for user %s\n", afsname));
 
diff --git a/source3/winbindd/winbindd_util.c b/source3/winbindd/winbindd_util.c
index 656735633b6..c36ae0bb0ac 100644
--- a/source3/winbindd/winbindd_util.c
+++ b/source3/winbindd/winbindd_util.c
@@ -931,7 +931,7 @@ void fill_domain_username(fstring name, const char *domain, const char *user, bo
 	fstring tmp_user;
 
 	fstrcpy(tmp_user, user);
-	strlower_m(tmp_user);
+	(void)strlower_m(tmp_user);
 
 	if (can_assume && assume_domain(domain)) {
 		strlcpy(name, tmp_user, sizeof(fstring));
@@ -954,7 +954,10 @@ char *fill_domain_username_talloc(TALLOC_CTX *mem_ctx,
 	char *tmp_user, *name;
 
 	tmp_user = talloc_strdup(mem_ctx, user);
-	strlower_m(tmp_user);
+	if (!strlower_m(tmp_user)) {
+		TALLOC_FREE(tmp_user);
+		return NULL;
+	}
 
 	if (can_assume && assume_domain(domain)) {
 		name = tmp_user;