diff --git a/lib/str_replace.h b/lib/str_replace.h
index 59d2d2f4cf..e112b4c6f2 100644
--- a/lib/str_replace.h
+++ b/lib/str_replace.h
@@ -33,7 +33,7 @@ extern size_t strlcat(char *dst, const char *src, size_t size);
 #endif
 
 #if !defined(HAVE_STRCASESTR)
-extern char *strcasestr(const char *s1, const char *s2);
+extern const char *strcasestr(const char *s1, const char *s2);
 #endif
 
 #endif