diff --git a/src/pystencilssfg/composer/gpu_composer.py b/src/pystencilssfg/composer/gpu_composer.py
index 06021dd9bd8e128cb2a84809ddbb67c2be43a51d..aaffb02820baabd93aead08db30a35b57851f3fd 100644
--- a/src/pystencilssfg/composer/gpu_composer.py
+++ b/src/pystencilssfg/composer/gpu_composer.py
@@ -167,7 +167,7 @@ class GpuInvocationBuilder:
         self._dim3 = gpu_api.dim3
 
         self._shared_memory_bytes: ExprLike = "0"
-        self._stream: ExprLike | None
+        self._stream: ExprLike | None = None
 
     @property
     def shared_memory_bytes(self) -> ExprLike: