diff --git a/renderdoc/serialise/serialiser.cpp b/renderdoc/serialise/serialiser.cpp
index ebe876582..3857aa2e9 100644
--- a/renderdoc/serialise/serialiser.cpp
+++ b/renderdoc/serialise/serialiser.cpp
@@ -1002,7 +1002,7 @@ Chunk::Chunk(Serialiser<SerialiserMode::Writing> &ser, uint16_t chunkType, Chunk
 byte *ChunkAllocator::AllocAlignedBuffer(uint64_t size)
 {
   // always allocate 64-bytes at a time even if the size is smaller
-  return AllocateFromPages(freeBufferPages, fullBufferPages, (size_t)AlignUp(size, 64ULL));
+  return AllocateFromPages(freeBufferPages, fullBufferPages, AlignUp((size_t)size, (size_t)64));
 }
 
 byte *ChunkAllocator::AllocChunk()