diff --git a/libc/string/strchr.c b/libc/string/strchr.c
index 93cb250..29acca5 100644
--- a/libc/string/strchr.c
+++ b/libc/string/strchr.c
@@ -47,5 +47,5 @@
 
 char *
 strchr(const char *p, int ch) {
-    return __strchr_chk(p, ch, (size_t) -1);
+    return __strchr_chk(p, ch, __BIONIC_FORTIFY_UNKNOWN_SIZE);
 }