diff --git a/loopy/target/pyopencl.py b/loopy/target/pyopencl.py
index ecaea9b57b27895eb30e175025fb7a19a08593eb..e4da6cd8baa0f379d8067688ec1bd670d64d84ce 100644
--- a/loopy/target/pyopencl.py
+++ b/loopy/target/pyopencl.py
@@ -888,7 +888,7 @@ class PyOpenCLPythonASTBuilder(PythonASTBuilderBase):
                     struct_overflow_arg_names)
 
             py_passed_args = []
-            struct_pack_types = []
+            struct_pack_types: list[str] = []
             struct_pack_args = []
 
             for arg_name in skai.passed_names: