diff --git a/bolt_windows.go b/bolt_windows.go
index 020f1a1..ec21ecb 100644
--- a/bolt_windows.go
+++ b/bolt_windows.go
@@ -72,7 +72,7 @@ func mmap(db *DB, sz int) error {
 			return fmt.Errorf("truncate: %s", err)
 		}
 		sizehi = uint32(sz >> 32)
-		sizelo = uint32(sz) & 0xffffffff
+		sizelo = uint32(sz)
 	}
 
 	// Open a file mapping handle.