diff --git a/loopy/target/__init__.py b/loopy/target/__init__.py
index be04d1008553f940532d6cd635000c2c1e0e9623..9e8211a03f00c60a76120f1cfb0493318984d2c8 100644
--- a/loopy/target/__init__.py
+++ b/loopy/target/__init__.py
@@ -216,7 +216,7 @@ class ASTBuilderBase(Generic[ASTType]):
     def get_function_declaration(
             self, codegen_state: CodeGenerationState,
             codegen_result: CodeGenerationResult, schedule_index: int
-            ) -> Tuple[Sequence[Tuple[str, str]], ASTType]:
+            ) -> Tuple[Sequence[Tuple[str, str]], Optional[ASTType]]:
         """Returns preambles and the AST for the function declaration."""
         raise NotImplementedError
 
diff --git a/loopy/target/pyopencl.py b/loopy/target/pyopencl.py
index 40963a85ee617247657d4f8793589310c76b874e..2742e472b5665f7675238991c7103d0397994b70 100644
--- a/loopy/target/pyopencl.py
+++ b/loopy/target/pyopencl.py
@@ -633,7 +633,7 @@ def generate_value_arg_setup(
 
     from genpy import If, Raise, Statement as S, Suite
 
-    result: List[str] = []
+    result: List[genpy.Generable] = []
     gen = result.append
 
     buf_indices_and_args = []
@@ -717,7 +717,7 @@ def generate_array_arg_setup(
     from loopy.kernel.array import ArrayBase
     from genpy import Statement as S, Suite
 
-    result: List[str] = []
+    result: List[genpy.Generable] = []
     gen = result.append
 
     cl_indices_and_args: List[Union[int, str]] = []
@@ -787,7 +787,7 @@ class PyOpenCLPythonASTBuilder(PythonASTBuilderBase):
     def get_function_declaration(
             self, codegen_state: CodeGenerationState,
             codegen_result: CodeGenerationResult, schedule_index: int
-            ) -> Tuple[Sequence[Tuple[str, str]], genpy.Generable]:
+            ) -> Tuple[Sequence[Tuple[str, str]], Optional[genpy.Generable]]:
         # no such thing in Python
         return [], None
 
diff --git a/loopy/target/python.py b/loopy/target/python.py
index f93d2b44ea21e19096778ed6fd3c37286a7c2ee7..1940dab1622afe7a879235bedf2265bb5afab33e 100644
--- a/loopy/target/python.py
+++ b/loopy/target/python.py
@@ -23,7 +23,7 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 """
 
-from typing import Tuple, Sequence
+from typing import Optional, Sequence, Tuple
 
 from pymbolic.mapper import Mapper
 from pymbolic.mapper.stringifier import StringifyMapper
@@ -169,7 +169,7 @@ class PythonASTBuilderBase(ASTBuilderBase[Generable]):
     def get_function_declaration(
             self, codegen_state: CodeGenerationState,
             codegen_result: CodeGenerationResult, schedule_index: int
-            ) -> Tuple[Sequence[Tuple[str, str]], None]:
+            ) -> Tuple[Sequence[Tuple[str, str]], Optional[Generable]]:
         return [], None
 
     def get_function_definition(self, codegen_state, codegen_result,