diff --git a/lib/libc/tests/string/Makefile b/lib/libc/tests/string/Makefile
--- a/lib/libc/tests/string/Makefile
+++ b/lib/libc/tests/string/Makefile
@@ -13,6 +13,7 @@
 ATF_TESTS_C+=		stpncpy_test
 ATF_TESTS_C+=		strcspn_test
 ATF_TESTS_C+=		strerror2_test
+ATF_TESTS_C+=		strspn_test
 ATF_TESTS_C+=		strverscmp_test
 ATF_TESTS_C+=		strxfrm_test
 ATF_TESTS_C+=		wcscasecmp_test
@@ -34,7 +35,6 @@
 NETBSD_ATF_TESTS_C+=	strlen_test
 NETBSD_ATF_TESTS_C+=	strpbrk_test
 NETBSD_ATF_TESTS_C+=	strrchr_test
-NETBSD_ATF_TESTS_C+=	strspn_test
 NETBSD_ATF_TESTS_C+=	swab_test
 
 SRCS.strerror2_test=	strerror_test.c
diff --git a/lib/libc/tests/string/strcspn_test.c b/lib/libc/tests/string/strcspn_test.c
--- a/lib/libc/tests/string/strcspn_test.c
+++ b/lib/libc/tests/string/strcspn_test.c
@@ -42,6 +42,12 @@
 
 enum { NOMATCH, MATCH };
 
+#ifdef STRSPN
+#define STRXSPN strspn
+#else
+#define STRXSPN strcspn
+#endif
+
 static void
 testcase(char *buf, size_t buflen, char *set, size_t setlen, int want_match)
 {
@@ -50,7 +56,11 @@
 	assert(setlen < UCHAR_MAX - 2);
 
 	for (i = 0; i < buflen; i++)
+#ifdef STRSPN
+		buf[i] = UCHAR_MAX - i % (setlen > 0 ? setlen : 1);
+#else /* strcspn */
 		buf[i] = 1 + i % (UCHAR_MAX - setlen - 1);
+#endif
 
 	buf[i] = '\0';
 
@@ -59,15 +69,25 @@
 
 	set[i] = '\0';
 
+#ifdef STRSPN
+	if (setlen == 0)
+		expected = 0;
+	else if (want_match == MATCH && buflen > 0) {
+		buf[buflen - 1] = 1;
+		expected = buflen - 1;
+	} else
+		expected = buflen;
+#else /* strcspn */
 	if (want_match == MATCH && buflen > 0 && setlen > 0) {
 		buf[buflen - 1] = UCHAR_MAX;
 		expected = buflen - 1;
 	} else
 		expected = buflen;
+#endif
 
-	outcome = strcspn(buf, set);
-	ATF_CHECK_EQ_MSG(expected, outcome, "strcspn(%p[%zu], %p[%zu]) = %zu != %zu",
-	    buf, buflen, set, setlen, outcome, expected);
+	outcome = STRXSPN(buf, set);
+	ATF_CHECK_EQ_MSG(expected, outcome, "%s(%p[%zu], %p[%zu]) = %zu != %zu",
+	    __XSTRING(STRXSPN), buf, buflen, set, setlen, outcome, expected);
 }
 
 /* test set with all alignments and lengths of buf */
diff --git a/lib/libc/tests/string/strspn_test.c b/lib/libc/tests/string/strspn_test.c
new file mode 100644
--- /dev/null
+++ b/lib/libc/tests/string/strspn_test.c
@@ -0,0 +1,30 @@
+/*-
+ * Copyright (c) 2023 The FreeBSD Foundation
+ *
+ * This software was developed by Robert Clausecker <fuz@FreeBSD.org>
+ * under sponsorship from the FreeBSD Foundation.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ''AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE
+ */
+
+#define STRSPN
+#include "strcspn_test.c"