diff --git a/src/lib/OpenEXRCore/chunk.c b/src/lib/OpenEXRCore/chunk.c
index 99a2b8bf5..ec3ed7777 100644
--- a/src/lib/OpenEXRCore/chunk.c
+++ b/src/lib/OpenEXRCore/chunk.c
@@ -565,7 +565,7 @@ extract_chunk_table (
     if (ctable == NULL)
     {
         int64_t      nread = 0;
-        uintptr_t    eptr = 0, nptr = 0;
+        uint64_t     eptr = 0, nptr = 0;
         int          complete = 1;
         uint64_t     maxoff   = ((uint64_t) -1);
         exr_result_t rv;
@@ -639,7 +639,7 @@ extract_chunk_table (
         }
         else { priv_to_native64 (ctable, part->chunk_count); }
 
-        nptr = (uintptr_t) ctable;
+        nptr = (uint64_t) ctable;
         // see if we win or not
         if (!atomic_compare_exchange_strong (
                 EXR_CONST_CAST (atomic_uintptr_t*, &(part->chunk_table)),