diff --git a/src/external/sinfl.h b/src/external/sinfl.h
index af730c1d2..591fcf1cb 100644
--- a/src/external/sinfl.h
+++ b/src/external/sinfl.h
@@ -171,9 +171,10 @@ extern int zsinflate(void *out, int cap, const void *in, int size);
 
 static int
 sinfl_bsr(unsigned n) {
-#if defined(_MSC_VER) && !defined(__clang__)
-  _BitScanReverse(&n, n);
-  return n;
+#ifdef _MSC_VER
+  unsigned long r = 0;
+  _BitScanReverse(&r, n);
+  return int(r);
 #else // defined(__GNUC__) || defined(__clang__) || defined(__TINYC__)
   return 31 - __builtin_clz(n);
 #endif