diff --git a/src/win32/mingw-compat.h b/src/win32/mingw-compat.h
index 97b1cb71b..fe0abfb54 100644
--- a/src/win32/mingw-compat.h
+++ b/src/win32/mingw-compat.h
@@ -21,7 +21,7 @@
 
 GIT_INLINE(size_t) p_strnlen(const char *s, size_t maxlen) {
 	const char *end = memchr(s, 0, maxlen);
-	return end ? (end - s) : maxlen;
+	return end ? (size_t)(end - s) : maxlen;
 }
 
 #endif