diff --git a/targettest/Makefile b/targettest/Makefile
index f3694335c..44933949a 100644
--- a/targettest/Makefile
+++ b/targettest/Makefile
@@ -160,6 +160,7 @@ EXELIST_c64 = \
 	scanf-test \
 	ser-test \
 	strdup-test \
+	strnlen \
 	stroserror-test \
 	strqtok-test \
 	tinyshell \
@@ -190,6 +191,7 @@ EXELIST_vic20 = \
 	rename-test \
 	scanf-test \
 	strdup-test \
+	strnlen \
 	stroserror-test \
 	strqtok-test \
 	tinyshell \
@@ -222,6 +224,7 @@ EXELIST_apple2 = \
 	seek \
 	ser-test \
 	strdup-test \
+	strnlen \
 	stroserror-test \
 	strqtok-test \
 	tinyshell \
@@ -257,6 +260,7 @@ EXELIST_atari = \
 	seek \
 	ser-test \
 	strdup-test \
+	strnlen \
 	stroserror-test \
 	strqtok-test \
 	tinyshell \
diff --git a/targettest/strnlen.c b/targettest/strnlen.c
new file mode 100644
index 000000000..d07b7628c
--- /dev/null
+++ b/targettest/strnlen.c
@@ -0,0 +1,32 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+const char * str = "0123456789";
+
+void
+check (size_t result, size_t expected)
+{
+    if (result != expected) {
+        printf ("Expected strnlen() to return %d, got %d.\n",
+                expected, result);
+        exit (EXIT_FAILURE);
+    }
+}
+
+int
+main (void)
+{
+    size_t  maxlen = strlen (str);
+    size_t  result;
+    size_t  expected;
+
+    for (expected = 0; expected < maxlen; expected++)
+        check (strnlen (str, expected), expected);
+
+    check (strnlen (str, maxlen << 1), maxlen);
+
+    printf ("strnlen() OK.\n");
+
+    return EXIT_SUCCESS;
+}