diff --git a/mozilla/netwerk/base/src/nsURLParsers.cpp b/mozilla/netwerk/base/src/nsURLParsers.cpp
index 0641e150d54..2b3739d6210 100644
--- a/mozilla/netwerk/base/src/nsURLParsers.cpp
+++ b/mozilla/netwerk/base/src/nsURLParsers.cpp
@@ -132,7 +132,7 @@ nsBaseURLParser::ParseURL(const char *spec, PRInt32 specLen,
     }
 
     // ignore trailing whitespace and control characters
-    for (p = spec + specLen - 1; (*p <= ' ') && (p != spec); --p);
+    for (p = spec + specLen - 1; ((unsigned char) *p <= ' ') && (p != spec); --p);
 
     specLen = p - spec + 1;