diff --git a/extension/pybindings/pybindings.cpp b/extension/pybindings/pybindings.cpp
index 69952c5d173..78fca25ed02 100644
--- a/extension/pybindings/pybindings.cpp
+++ b/extension/pybindings/pybindings.cpp
@@ -757,7 +757,9 @@ struct PyModule final {
       } else if (py::isinstance<py::int_>(python_input)) {
         cpp_inputs.push_back(EValue(py::cast<int64_t>(python_input)));
       } else {
-        ET_ASSERT_UNREACHABLE_MSG("Unsupported pytype: %s", type_str.c_str());
+        throw std::runtime_error(
+            "Unsupported python type " + type_str +
+            ". Ensure that inputs are passed as a flat list of tensors.");
       }
     }
 
diff --git a/extension/pybindings/test/make_test.py b/extension/pybindings/test/make_test.py
index 32a695b99e2..f3087d112ed 100644
--- a/extension/pybindings/test/make_test.py
+++ b/extension/pybindings/test/make_test.py
@@ -464,6 +464,16 @@ def test_verification_config(tester) -> None:
 
                 tester.assertEqual(str(expected), str(executorch_output))
 
+        def test_unsupported_input_type(tester):
+            exported_program, inputs = create_program(ModuleAdd())
+            executorch_module = load_fn(exported_program.buffer)
+
+            # Pass an unsupported input type to the module.
+            inputs = ([*inputs],)
+
+            # This should raise a Python error, not hit a fatal assert in the C++ code.
+            tester.assertRaises(RuntimeError, executorch_module, inputs)
+
         ######### RUN TEST CASES #########
         test_e2e(tester)
         test_multiple_entry(tester)
@@ -479,5 +489,6 @@ def test_verification_config(tester) -> None:
         test_method_meta(tester)
         test_bad_name(tester)
         test_verification_config(tester)
+        test_unsupported_input_type(tester)
 
     return wrapper