diff --git a/Library/OcApfsLib/OcApfsIo.c b/Library/OcApfsLib/OcApfsIo.c
index 393349e6..9c1b4271 100644
--- a/Library/OcApfsLib/OcApfsIo.c
+++ b/Library/OcApfsLib/OcApfsIo.c
@@ -224,7 +224,8 @@ ApfsReadDriver (
       &Lba
       );
 
-    if (OcOverflowMulUN (JumpStart->RecordExtents[Index].BlockCount, PrivateData->ApfsBlockSize, &ChunkSize)
+    if (JumpStart->RecordExtents[Index].BlockCount > MAX_UINTN
+      || OcOverflowMulUN ((UINTN) JumpStart->RecordExtents[Index].BlockCount, PrivateData->ApfsBlockSize, &ChunkSize)
       || ChunkSize > EfiFileSize) {
       FreePool (EfiFile);
       return EFI_SECURITY_VIOLATION;