diff --git a/loopy/target/c/c_execution.py b/loopy/target/c/c_execution.py
index 501db3dfdaa7d73559efc854826c6f8ade733799..fd06eb0e88059c23ba56828c54eee4decb1d1582 100644
--- a/loopy/target/c/c_execution.py
+++ b/loopy/target/c/c_execution.py
@@ -52,10 +52,7 @@ class CExecutionWrapperGenerator(ExecutionWrapperGeneratorBase):
         super(CExecutionWrapperGenerator, self).__init__(system_args)
 
     def python_dtype_str(self, dtype):
-        # TODO: figure out why isbuiltin isn't working in test (requiring second
-        # line)
-        if dtype.isbuiltin or \
-                np.dtype(str(dtype)).isbuiltin:
+        if np.dtype(str(dtype)).isbuiltin:
             return "_lpy_np."+dtype.name
         raise Exception('dtype: {} not recognized'.format(dtype))