diff --git a/Python/hamt.c b/Python/hamt.c
index 3841259..5efc8d7 100644
--- a/Python/hamt.c
+++ b/Python/hamt.c
@@ -1864,7 +1864,7 @@
                     continue;
                 }
 
-                bitmap |= 1 << i;
+                bitmap |= 1U << i;
 
                 if (IS_BITMAP_NODE(node)) {
                     PyHamtNode_Bitmap *child = (PyHamtNode_Bitmap *)node;