diff --git a/src/pystencilssfg/composer/gpu_composer.py b/src/pystencilssfg/composer/gpu_composer.py
index 72628abb2609aad7d7d3719fbf98bfb5d45c8de5..a1d01c4066b879d7d23c0850e17cece49dcfb759 100644
--- a/src/pystencilssfg/composer/gpu_composer.py
+++ b/src/pystencilssfg/composer/gpu_composer.py
@@ -186,13 +186,8 @@ class SfgGpuComposer(SfgComposerMixIn):
 
                 block_size_init_args: tuple[ExprLike, ...]
                 if user_block_size is None:
-                    if launch_config.block_size is None:
-                        raise ValueError(
-                            "Neither a user-defined nor a default block size was defined."
-                        )
-
                     block_size_init_args = tuple(
-                        str(bs) for bs in launch_config.block_size
+                        str(bs) for bs in launch_config.default_block_size
                     )
                 else:
                     block_size_init_args = (user_block_size,)