diff --git a/js/src/jsregexp.c b/js/src/jsregexp.c
index e5210bec495f..0b98cc1db912 100644
--- a/js/src/jsregexp.c
+++ b/js/src/jsregexp.c
@@ -353,22 +353,33 @@ typedef struct REGlobalData {
  *    code point value is less than decimal 128, then return ch.
  * 6. Return cu.
  */
-static jschar
-upcase(jschar ch)
+static uintN
+upcase(uintN ch)
 {
-    jschar cu = JS_TOUPPER(ch);
-    if (ch >= 128 && cu < 128)
+    uintN cu;
+
+    JS_ASSERT((uintN) (jschar) ch == ch);
+    if (ch < 128) {
+        if (ch - (uintN) 'a' <= (uintN) ('z' - 'a'))
+            ch -= (uintN) ('a' - 'A');
         return ch;
-    return cu;
+    }
+
+    cu = JS_TOUPPER(ch);
+    return (cu < 128) ? ch : cu;
 }
 
-static jschar
-downcase(jschar ch)
+static uintN
+downcase(uintN ch)
 {
-    jschar cl = JS_TOLOWER(ch);
-    if (cl >= 128 && ch < 128)
+    JS_ASSERT((uintN) (jschar) ch == ch);
+    if (ch < 128) {
+        if (ch - (uintN) 'A' <= (uintN) ('Z' - 'A'))
+            ch += (uintN) ('a' - 'A');
         return ch;
-    return cl;
+    }
+
+    return JS_TOLOWER(ch);
 }
 
 /* Construct and initialize an RENode, returning NULL for out-of-memory */
@@ -944,7 +955,7 @@ CalculateBitmapSize(CompilerState *state, RENode *target, const jschar *src,
                 break;
               case 'c':
                 if (src < end && RE_IS_LETTER(*src)) {
-                    localMax = (jschar) (*src++ & 0x1F);
+                    localMax = (uintN) (*src++) & 0x1F;
                 } else {
                     --src;
                     localMax = '\\';
@@ -1044,7 +1055,7 @@ lexHex:
             break;
         }
         if (state->flags & JSREG_FOLD) {
-            c = JS_MAX(upcase((jschar) localMax), downcase((jschar) localMax));
+            c = (jschar) JS_MAX(upcase(localMax), downcase(localMax));
             if (c > localMax)
                 localMax = c;
         }
@@ -2220,12 +2231,12 @@ AddCharacterToCharSet(RECharSet *cs, jschar c)
 
 /* Add a character range, c1 to c2 (inclusive) to the RECharSet */
 static void
-AddCharacterRangeToCharSet(RECharSet *cs, jschar c1, jschar c2)
+AddCharacterRangeToCharSet(RECharSet *cs, uintN c1, uintN c2)
 {
     uintN i;
 
-    uintN byteIndex1 = (uintN)(c1 >> 3);
-    uintN byteIndex2 = (uintN)(c2 >> 3);
+    uintN byteIndex1 = c1 >> 3;
+    uintN byteIndex2 = c2 >> 3;
 
     JS_ASSERT((c2 <= cs->length) && (c1 <= c2));