diff --git a/llvm/include/llvm/Bitstream/BitstreamWriter.h b/llvm/include/llvm/Bitstream/BitstreamWriter.h
index d5593d6ea9f05..8dc135e6404da 100644
--- a/llvm/include/llvm/Bitstream/BitstreamWriter.h
+++ b/llvm/include/llvm/Bitstream/BitstreamWriter.h
@@ -158,7 +158,7 @@ class BitstreamWriter {
     // Copy data to update into Bytes from the file FS and the buffer Out.
     char Bytes[8];
     size_t BytesNum = StartBit ? 8 : 4;
-    size_t BytesFromDisk = std::min(BytesNum, NumOfFlushedBytes - ByteNo);
+    size_t BytesFromDisk = std::min(static_cast<uint64_t>(BytesNum), NumOfFlushedBytes - ByteNo);
     size_t BytesFromBuffer = BytesNum - BytesFromDisk;
 
     // When unaligned, copy existing data into Bytes from the file FS and the