diff --git a/coccinelle/strjoina.cocci b/coccinelle/strjoina.cocci
new file mode 100644
index 00000000000..a6236eb0f96
--- /dev/null
+++ b/coccinelle/strjoina.cocci
@@ -0,0 +1,6 @@
+@@
+expression n, m;
+expression list s;
+@@
+- n = strjoina(m, s, NULL);
++ n = strjoina(m, s);
diff --git a/src/core/unit.c b/src/core/unit.c
index 49c990c2d7d..c60ae2be9dd 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -2518,12 +2518,11 @@ int unit_install_bus_match(Unit *u, sd_bus *bus, const char *name) {
                 return -EBUSY;
 
         match = strjoina("type='signal',"
-                        "sender='org.freedesktop.DBus',"
-                        "path='/org/freedesktop/DBus',"
-                        "interface='org.freedesktop.DBus',"
-                        "member='NameOwnerChanged',"
-                        "arg0='", name, "'",
-                        NULL);
+                         "sender='org.freedesktop.DBus',"
+                         "path='/org/freedesktop/DBus',"
+                         "interface='org.freedesktop.DBus',"
+                         "member='NameOwnerChanged',"
+                         "arg0='", name, "'");
 
         return sd_bus_add_match(bus, &u->match_bus_slot, match, signal_name_owner_changed, u);
 }
@@ -3437,7 +3436,7 @@ int unit_write_drop_in_private(Unit *u, UnitSetPropertiesMode mode, const char *
         if (!IN_SET(mode, UNIT_PERSISTENT, UNIT_RUNTIME))
                 return 0;
 
-        ndata = strjoina("[", UNIT_VTABLE(u)->private_section, "]\n", data, NULL);
+        ndata = strjoina("[", UNIT_VTABLE(u)->private_section, "]\n", data);
 
         return unit_write_drop_in(u, mode, name, ndata);
 }
diff --git a/src/coredump/coredump.c b/src/coredump/coredump.c
index 085909c20c2..f65cb6f9dd7 100644
--- a/src/coredump/coredump.c
+++ b/src/coredump/coredump.c
@@ -1095,7 +1095,7 @@ static int process_kernel(int argc, char* argv[]) {
                         IOVEC_SET_STRING(iovec[n_iovec++], core_environ);
         }
 
-        core_timestamp = strjoina("COREDUMP_TIMESTAMP=", context[CONTEXT_TIMESTAMP], "000000", NULL);
+        core_timestamp = strjoina("COREDUMP_TIMESTAMP=", context[CONTEXT_TIMESTAMP], "000000");
         IOVEC_SET_STRING(iovec[n_iovec++], core_timestamp);
 
         IOVEC_SET_STRING(iovec[n_iovec++], "MESSAGE_ID=fc2e22bc6ee647b6b90729ab34a250b1");
diff --git a/src/login/logind-session.c b/src/login/logind-session.c
index e088225bebb..676fbc15a3f 100644
--- a/src/login/logind-session.c
+++ b/src/login/logind-session.c
@@ -513,7 +513,7 @@ static int session_start_scope(Session *s) {
                 if (!scope)
                         return log_oom();
 
-                description = strjoina("Session ", s->id, " of user ", s->user->name, NULL);
+                description = strjoina("Session ", s->id, " of user ", s->user->name);
 
                 r = manager_start_scope(
                                 s->manager,
diff --git a/src/machine/machine-dbus.c b/src/machine/machine-dbus.c
index c7ff0efac8f..ab54d9e9342 100644
--- a/src/machine/machine-dbus.c
+++ b/src/machine/machine-dbus.c
@@ -730,7 +730,7 @@ int bus_machine_method_open_shell(sd_bus_message *message, void *userdata, sd_bu
                 return r;
 
         /* Name and mode */
-        unit = strjoina("container-shell@", p, ".service", NULL);
+        unit = strjoina("container-shell@", p, ".service");
         r = sd_bus_message_append(tm, "ss", unit, "fail");
         if (r < 0)
                 return r;
diff --git a/src/resolve/resolved-dns-dnssec.c b/src/resolve/resolved-dns-dnssec.c
index 0af75514252..a54aed3a63c 100644
--- a/src/resolve/resolved-dns-dnssec.c
+++ b/src/resolve/resolved-dns-dnssec.c
@@ -1734,7 +1734,7 @@ static int dnssec_nsec_covers_wildcard(DnsResourceRecord *rr, const char *name)
         if (r <= 0)
                 return r;
 
-        wc = strjoina("*.", common_suffix, NULL);
+        wc = strjoina("*.", common_suffix);
         return dns_name_between(dns_resource_key_name(rr->key), wc, rr->nsec.next_domain_name);
 }
 
diff --git a/src/shared/bus-util.c b/src/shared/bus-util.c
index 0caaca03c75..2b86b1fcd63 100644
--- a/src/shared/bus-util.c
+++ b/src/shared/bus-util.c
@@ -2050,8 +2050,8 @@ static void log_job_error_with_service_result(const char* service, const char *r
                 _cleanup_free_ char *t;
 
                 t = strv_join((char**) extra_args, " ");
-                systemctl = strjoina("systemctl ", t ?: "<args>", NULL);
-                journalctl = strjoina("journalctl ", t ?: "<args>", NULL);
+                systemctl = strjoina("systemctl ", t ? : "<args>");
+                journalctl = strjoina("journalctl ", t ? : "<args>");
         }
 
         if (!isempty(result)) {
diff --git a/src/shared/path-lookup.c b/src/shared/path-lookup.c
index ca69a0aef29..167108ee1bf 100644
--- a/src/shared/path-lookup.c
+++ b/src/shared/path-lookup.c
@@ -249,7 +249,7 @@ static int acquire_generator_dirs(
                 if (!e)
                         return -ENXIO;
 
-                prefix = strjoina(e, "/systemd/", NULL);
+                prefix = strjoina(e, "/systemd/");
                 break;
         }
 
diff --git a/src/systemctl/systemctl.c b/src/systemctl/systemctl.c
index f0e788a5085..65b52be04a3 100644
--- a/src/systemctl/systemctl.c
+++ b/src/systemctl/systemctl.c
@@ -3254,7 +3254,7 @@ static int kill_unit(int argc, char *argv[], void *userdata) {
 
         /* --fail was specified */
         if (streq(arg_job_mode, "fail"))
-                kill_who = strjoina(arg_kill_who, "-fail", NULL);
+                kill_who = strjoina(arg_kill_who, "-fail");
 
         r = expand_names(bus, strv_skip(argv, 1), NULL, &names);
         if (r < 0)