diff --git a/tools/regression/lib/libc/locale/test-btowc.c b/tools/regression/lib/libc/locale/test-btowc.c
index 9ed45821e3a..b01c04344aa 100644
--- a/tools/regression/lib/libc/locale/test-btowc.c
+++ b/tools/regression/lib/libc/locale/test-btowc.c
@@ -39,6 +39,7 @@ __FBSDID("$FreeBSD$");
 #include <locale.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <wchar.h>
 
 int
diff --git a/tools/regression/lib/libc/locale/test-iswctype.c b/tools/regression/lib/libc/locale/test-iswctype.c
index ca9621a7d34..1c56b887422 100644
--- a/tools/regression/lib/libc/locale/test-iswctype.c
+++ b/tools/regression/lib/libc/locale/test-iswctype.c
@@ -37,6 +37,7 @@ __FBSDID("$FreeBSD$");
 #include <assert.h>
 #include <locale.h>
 #include <stdio.h>
+#include <string.h>
 #include <wchar.h>
 #include <wctype.h>
 
diff --git a/tools/regression/lib/libc/locale/test-towctrans.c b/tools/regression/lib/libc/locale/test-towctrans.c
index 6c0e428db65..fabb343bc6d 100644
--- a/tools/regression/lib/libc/locale/test-towctrans.c
+++ b/tools/regression/lib/libc/locale/test-towctrans.c
@@ -37,6 +37,7 @@ __FBSDID("$FreeBSD$");
 #include <assert.h>
 #include <locale.h>
 #include <stdio.h>
+#include <string.h>
 #include <wchar.h>
 #include <wctype.h>