diff --git a/galsim/config/process.py b/galsim/config/process.py
index e9ce33537c..fe4882feb8 100644
--- a/galsim/config/process.py
+++ b/galsim/config/process.py
@@ -265,7 +265,7 @@ def Process(config, logger=None, njobs=1, job=1, new_params=None, except_abort=F
                  json.dumps(config, default=lambda o: repr(o), indent=4))
 
     # Warn about any unexpected fields.
-    unexpected = [ k for k in config if k not in top_level_fields ]
+    unexpected = [ k for k in config if k not in top_level_fields and k[0] != '_' ]
     if len(unexpected) > 0 and logger:
         logger.warning("Warning: config dict contains the following unexpected fields: %s.",
                        unexpected)
diff --git a/galsim/config/value_eval.py b/galsim/config/value_eval.py
index 0ed5687d82..9294b34daa 100644
--- a/galsim/config/value_eval.py
+++ b/galsim/config/value_eval.py
@@ -86,7 +86,7 @@ def _GenerateFromEval(config, base, value_type):
 
         # These will be the variables to use for evaluating the eval statement.
         # Start with the current locals and globals, and add extra items to them.
-        if 'eval_gdict' not in base:
+        if '_eval_gdict' not in base:
             gdict = globals().copy()
             # We allow the following modules to be used in the eval string:
             exec('import galsim', gdict)
@@ -95,9 +95,9 @@ def _GenerateFromEval(config, base, value_type):
             exec('import numpy as np', gdict)
             exec('import os', gdict)
             ImportModules(base, gdict)
-            base['eval_gdict'] = gdict
+            base['_eval_gdict'] = gdict
         else:
-            gdict = base['eval_gdict']
+            gdict = base['_eval_gdict']
 
         if 'str' not in config:
             raise GalSimConfigError(