diff --git a/OpenEXR/IlmImf/ImfTiledMisc.cpp b/OpenEXR/IlmImf/ImfTiledMisc.cpp
index c9e8731f11..b8e195fd86 100644
--- a/OpenEXR/IlmImf/ImfTiledMisc.cpp
+++ b/OpenEXR/IlmImf/ImfTiledMisc.cpp
@@ -301,10 +301,8 @@ calculateNumTiles (int *numTiles,
 {
     for (int i = 0; i < numLevels; i++)
     {
-        int l = levelSize (min, max, i, rmode);
-        if (l > std::numeric_limits<int>::max() - size + 1)
-            throw IEX_NAMESPACE::ArgExc ("Invalid size.");
-
+        // use 64 bits to avoid int overflow if size is large.
+        Int64 l = levelSize (min, max, i, rmode);
         numTiles[i] = (l + size - 1) / size;
     }
 }