diff --git a/OpenEXR/IlmImf/ImfTiledMisc.cpp b/OpenEXR/IlmImf/ImfTiledMisc.cpp
index 8552ada207..51b6e5c267 100644
--- a/OpenEXR/IlmImf/ImfTiledMisc.cpp
+++ b/OpenEXR/IlmImf/ImfTiledMisc.cpp
@@ -301,7 +301,11 @@ calculateNumTiles (int *numTiles,
 {
     for (int i = 0; i < numLevels; i++)
     {
-	numTiles[i] = (levelSize (min, max, i, rmode) + size - 1) / size;
+        int l = levelSize (min, max, i, rmode);
+        if (l > std::numeric_limits<int>::max() - size + 1)
+            throw IEX_NAMESPACE::ArgExc ("Invalid size.");
+
+        numTiles[i] = (l + size - 1) / size;
     }
 }