diff --git a/layout/style/nsCSSScanner.cpp b/layout/style/nsCSSScanner.cpp
index d0dec735c0a..51317ec5ff9 100644
--- a/layout/style/nsCSSScanner.cpp
+++ b/layout/style/nsCSSScanner.cpp
@@ -250,7 +250,7 @@ PR_STATIC_CALLBACK(int) CSSErrorsPrefChanged(const char *aPref, void *aClosure)
 }
 
 void nsCSSScanner::Init(nsIUnicharInputStream* aInput, 
-                        const PRUnichar * aBuffer, PRInt32 aCount, 
+                        const PRUnichar * aBuffer, PRUint32 aCount, 
                         nsIURI* aURI, PRUint32 aLineNumber)
 {
   NS_PRECONDITION(!mInputStream, "Should not have an existing input stream!");
@@ -473,16 +473,13 @@ PRInt32 nsCSSScanner::Read(nsresult& aErrorCode)
   if (0 < mPushbackCount) {
     rv = PRInt32(mPushback[--mPushbackCount]);
   } else {
-    if (mCount < 0) {
-      return -1;
-    }
     if (mOffset == mCount) {
       mOffset = 0;
       if (!mInputStream) {
         mCount = 0;
         return -1;
       }
-      aErrorCode = mInputStream->Read(mBuffer, CSS_BUFFER_SIZE, (PRUint32*)&mCount);
+      aErrorCode = mInputStream->Read(mBuffer, CSS_BUFFER_SIZE, &mCount);
       if (NS_FAILED(aErrorCode) || mCount == 0) {
         mCount = 0;
         return -1;
diff --git a/layout/style/nsCSSScanner.h b/layout/style/nsCSSScanner.h
index 12fb1b7f705..c053e2704fc 100644
--- a/layout/style/nsCSSScanner.h
+++ b/layout/style/nsCSSScanner.h
@@ -139,7 +139,7 @@ class nsCSSScanner {
   // when the line number is unknown.
   // Either aInput or (aBuffer and aCount) must be set.
   void Init(nsIUnicharInputStream* aInput, 
-            const PRUnichar *aBuffer, PRInt32 aCount, 
+            const PRUnichar *aBuffer, PRUint32 aCount,
             nsIURI* aURI, PRUint32 aLineNumber);
   void Close();
 
@@ -225,8 +225,8 @@ protected:
   PRUnichar mBuffer[CSS_BUFFER_SIZE];
 
   const PRUnichar *mReadPointer;
-  PRInt32 mOffset;
-  PRInt32 mCount;
+  PRUint32 mOffset;
+  PRUint32 mCount;
   PRUnichar* mPushback;
   PRInt32 mPushbackCount;
   PRInt32 mPushbackSize;