diff --git a/openbsd-compat/openbsd-compat.h b/openbsd-compat/openbsd-compat.h
index 957213577..f58646886 100644
--- a/openbsd-compat/openbsd-compat.h
+++ b/openbsd-compat/openbsd-compat.h
@@ -109,6 +109,10 @@ size_t strlcat(char *dst, const char *src, size_t siz);
 char *strcasestr(const char *, const char *);
 #endif
 
+#ifndef HAVE_STRNLEN
+size_t strnlen(const char *, size_t);
+#endif
+
 #ifndef HAVE_STRNDUP
 char *strndup(const char *s, size_t n);
 #endif