diff --git a/src/stpipe/step.py b/src/stpipe/step.py
index 7e780631..ca7c8cee 100644
--- a/src/stpipe/step.py
+++ b/src/stpipe/step.py
@@ -1377,7 +1377,7 @@ def build_config(cls, input, **kwargs):  # noqa: A002
         if "config_file" in kwargs:
             config_file = kwargs["config_file"]
             del kwargs["config_file"]
-            config_from_file = config_parser.load_config_file(config_file)
+            config_from_file = config_parser.load_config_file(str(config_file))
             config_parser.merge_config(config, config_from_file)
             config_dir = os.path.dirname(config_file)
         else:
diff --git a/tests/test_step.py b/tests/test_step.py
index 6a7ee36a..d4bfe9f3 100644
--- a/tests/test_step.py
+++ b/tests/test_step.py
@@ -284,9 +284,13 @@ def test_step_list_args(config_file_list_arg_step):
     correctly.
     """
     config, returned_config_file = ListArgStep.build_config(
-        "science.fits", config_file=str(config_file_list_arg_step)
+        "science.fits", config_file=config_file_list_arg_step
     )
-    assert returned_config_file == str(config_file_list_arg_step)
+    assert returned_config_file == config_file_list_arg_step
+
+    # Command line tests below need the config file path to be a string
+    returned_config_file = str(returned_config_file)
+
     c, *_ = cmdline.just_the_step_from_cmdline(
         [
             "filename.fits",