diff --git a/src/internal.c b/src/internal.c
index d5cf35026..b0e5b086b 100644
--- a/src/internal.c
+++ b/src/internal.c
@@ -12417,8 +12417,8 @@ static byte MaskMac(const byte* data, int sz, int macSz, byte* expMac)
     unsigned char started, notEnded;
     unsigned char good = 0;
 
-    if (scanStart < 0)
-        scanStart = 0;
+    scanStart &= (~scanStart) >> (sizeof(int) * 8 - 1);
+    macStart &= (~macStart) >> (sizeof(int) * 8 - 1);
 
     /* Div on Intel has different speeds depending on value.
      * Use a bitwise AND or mod a specific value (converted to mul). */