diff --git a/src/panfrost/lib/gen_pack.py b/src/panfrost/lib/gen_pack.py
index c70b8b3a6e9..bb17bd53ffd 100644
--- a/src/panfrost/lib/gen_pack.py
+++ b/src/panfrost/lib/gen_pack.py
@@ -78,7 +78,7 @@ __gen_sint(int32_t v, uint32_t start, uint32_t end)
    }
 #endif
 
-   return ((uint32_t) v) << start;
+   return (((uint32_t) v) << start) & ((2ll << end) - 1);
 }
 
 static inline uint32_t