diff --git a/cache.h b/cache.h
index 849bc0dcdd..5cc116ba42 100644
--- a/cache.h
+++ b/cache.h
@@ -1264,8 +1264,8 @@ static inline unsigned int hexval(unsigned char c)
  */
 static inline int hex2chr(const char *s)
 {
-	int val = hexval(s[0]);
-	return (val < 0) ? val : (val << 4) | hexval(s[1]);
+	unsigned int val = hexval(s[0]);
+	return (val & ~0xf) ? val : (val << 4) | hexval(s[1]);
 }
 
 /* Convert to/from hex/sha1 representation */