diff --git a/lib/nghttp3_ringbuf.c b/lib/nghttp3_ringbuf.c
index 75ef7ad..5e7775f 100644
--- a/lib/nghttp3_ringbuf.c
+++ b/lib/nghttp3_ringbuf.c
@@ -33,7 +33,7 @@
 
 #include "nghttp3_macro.h"
 
-#if defined(_MSC_VER) && (defined(_M_ARM) || defined(_M_ARM64))
+#if defined(_MSC_VER) && !defined(__clang__) && (defined(_M_ARM) || defined(_M_ARM64))
 unsigned int __popcnt(unsigned int x) {
   unsigned int c = 0;
   for (; x; ++c) {