diff --git a/libc/bionic/wchar.cpp b/libc/bionic/wchar.cpp
index 4e62f61..e466c91 100644
--- a/libc/bionic/wchar.cpp
+++ b/libc/bionic/wchar.cpp
@@ -173,7 +173,7 @@
   size_t o = 0; // Number of output characters written.
   for (; i < n && (*src)[i] != 0; ++i) {
     // TODO: UTF-8 support.
-    if ((*src)[i] > 0x7f) {
+    if (static_cast<uint8_t>((*src)[i]) > 0x7f) {
       errno = EILSEQ;
       if (dst != NULL) {
         *src = &(*src)[i];