diff --git a/pythonbpf/functions_pass.py b/pythonbpf/functions_pass.py
index 7b3a95d..fc3ddc3 100644
--- a/pythonbpf/functions_pass.py
+++ b/pythonbpf/functions_pass.py
@@ -674,7 +674,7 @@ def infer_return_type(func_node: ast.FunctionDef):
             if found_type is None:
                 found_type = t
             elif found_type != t:
-                raise ValueError(f"Conflicting return types:{found_type} vs {t}")
+                raise ValueError(f"Conflicting return types: {found_type} vs {t}")
     return found_type or "None"