diff --git a/vyper/codegen/function_definitions/external_function.py b/vyper/codegen/function_definitions/external_function.py
index 5539c78e96..2013c8cd73 100644
--- a/vyper/codegen/function_definitions/external_function.py
+++ b/vyper/codegen/function_definitions/external_function.py
@@ -171,6 +171,8 @@ def generate_ir_for_external_function(code, compilation_target):
     metadata required for `module.py` to construct the selector table.
     """
     func_t = code._metadata["func_type"]
+    assert func_t.is_external or func_t.is_constructor  # sanity check
+
     context = initialize_context(func_t, compilation_target, func_t.is_constructor)
     nonreentrant_pre, nonreentrant_post = get_nonreentrant_lock(func_t)
 
diff --git a/vyper/codegen/function_definitions/internal_function.py b/vyper/codegen/function_definitions/internal_function.py
index 3bb540980c..e79cce251f 100644
--- a/vyper/codegen/function_definitions/internal_function.py
+++ b/vyper/codegen/function_definitions/internal_function.py
@@ -41,6 +41,9 @@ def generate_ir_for_internal_function(
 
     func_t = code._metadata["func_type"]
 
+    # sanity check
+    assert func_t.is_internal or func_t.is_constructor
+
     context = initialize_context(func_t, module_ctx, is_ctor_context)
 
     for arg in func_t.arguments: