diff --git a/mozilla/netwerk/cache/src/nsDiskCacheDevice.cpp b/mozilla/netwerk/cache/src/nsDiskCacheDevice.cpp
index 98af24e9429..e00f1f2ed4e 100644
--- a/mozilla/netwerk/cache/src/nsDiskCacheDevice.cpp
+++ b/mozilla/netwerk/cache/src/nsDiskCacheDevice.cpp
@@ -676,10 +676,11 @@ nsDiskCacheDevice::OnDataSizeChange(nsCacheEntry * entry, PRInt32 deltaSize)
     NS_ASSERTION(binding->mRecord.ValidRecord(), "bad record");
 
     PRUint32  newSize = entry->DataSize() + deltaSize;
-    if (newSize > mCacheCapacity) {
+    PRUint32  maxSize = PR_MIN(mCacheCapacity / 2, kMaxDataFileSize);
+    if (newSize > maxSize) {
         nsresult rv = nsCacheService::DoomEntry(entry);
         NS_ASSERTION(NS_SUCCEEDED(rv),"DoomEntry() failed.");
-        return rv;
+        return NS_ERROR_ABORT;
     }
 
     PRUint32  sizeK = ((entry->DataSize() + 0x03FF) >> 10); // round up to next 1k
diff --git a/mozilla/netwerk/cache/src/nsDiskCacheMap.h b/mozilla/netwerk/cache/src/nsDiskCacheMap.h
index 1616bcdea41..71fc77ee035 100644
--- a/mozilla/netwerk/cache/src/nsDiskCacheMap.h
+++ b/mozilla/netwerk/cache/src/nsDiskCacheMap.h
@@ -61,14 +61,15 @@ struct nsDiskCacheEntry;
  *      2 = 1k block file
  *      3 = 4k block file
  *
- *  eFileSizeMask note:  Files larger than 64 Mb have zero size stored in the
+ *  eFileSizeMask note:  Files larger than 64 MiB have zero size stored in the
  *                       location.  The file itself must be examined to determine
- *                       its actual size.
+ *                       its actual size.  (XXX This is broken in places -darin)
  *
  *****************************************************************************/
 
 #define BLOCK_SIZE_FOR_INDEX(index)  ((index) ? (256 << (2 * ((index) - 1))) : 0)
-#define kSeparateFile   0
+#define kSeparateFile      0
+#define kMaxDataFileSize   0x4000000   // 64 MiB
 
 class nsDiskCacheRecord {