diff --git a/defs.h b/defs.h
index c20fcc61..bb4003f5 100644
--- a/defs.h
+++ b/defs.h
@@ -52,7 +52,10 @@
 #include <unistd.h>
 #include <stdlib.h>
 #include <stdio.h>
-#include <ctype.h>
+/* Open-coding isprint(ch) et al proved more efficient than calling
+ * generalized libc interface. We don't *want* to do non-ASCII anyway.
+ */
+/* #include <ctype.h> */
 #include <string.h>
 #include <errno.h>
 #include <signal.h>
diff --git a/file.c b/file.c
index cfdd0bb9..2af14bff 100644
--- a/file.c
+++ b/file.c
@@ -2456,7 +2456,7 @@ print_xattr_val(struct tcb *tcp, int failed,
 			unsigned char *in = &buf[3 * size];
 			size_t i;
 			for (i = 0; i < size; ++i) {
-				if (isprint(in[i]))
+				if (in[i] >= ' ' && in[i] <= 0x7e)
 					*out++ = in[i];
 				else {
 #define tohex(n) "0123456789abcdef"[n]
diff --git a/util.c b/util.c
index 0cc43feb..84ab00eb 100644
--- a/util.c
+++ b/util.c
@@ -400,7 +400,16 @@ string_quote(const char *instr, char *outstr, long len, int size)
 			/* Check for NUL-terminated string. */
 			if (c == eol)
 				break;
-			if (!isprint(c) && !isspace(c)) {
+
+			/* Force hex unless c is printable or whitespace */
+			if (c > 0x7e) {
+				usehex = 1;
+				break;
+			}
+			/* In ASCII isspace is only these chars: "\t\n\v\f\r".
+			 * They happen to have ASCII codes 9,10,11,12,13.
+			 */
+			if (c < ' ' && (unsigned)(c - 9) >= 5) {
 				usehex = 1;
 				break;
 			}
@@ -453,7 +462,7 @@ string_quote(const char *instr, char *outstr, long len, int size)
 					*s++ = 'v';
 					break;
 				default:
-					if (isprint(c))
+					if (c >= ' ' && c <= 0x7e)
 						*s++ = c;
 					else {
 						/* Print \octal */