--- a/widget/xpwidgets/GfxDriverInfo.h
+++ b/widget/xpwidgets/GfxDriverInfo.h
@@ -144,18 +144,18 @@ V(uint32_t a, uint32_t b, uint32_t c, ui
 }
 
 // All destination string storage needs to have at least 5 bytes available.
 inline bool SplitDriverVersion(const char *aSource, char *aAStr, char *aBStr, char *aCStr, char *aDStr)
 {
   // sscanf doesn't do what we want here to we parse this manually.
   int len = strlen(aSource);
   char *dest[4] = { aAStr, aBStr, aCStr, aDStr };
-  int destIdx = 0;
-  int destPos = 0;
+  unsigned destIdx = 0;
+  unsigned destPos = 0;
 
   for (int i = 0; i < len; i++) {
     if (destIdx > ArrayLength(dest)) {
       // Invalid format found. Ensure we don't access dest beyond bounds.
       return false;
     }
 
     if (aSource[i] == '.') {