diff --git a/src/optional/python/gnuparallel/_loader.py b/src/optional/python/gnuparallel/_loader.py
index 24a6ca6a..afee6a64 100755
--- a/src/optional/python/gnuparallel/_loader.py
+++ b/src/optional/python/gnuparallel/_loader.py
@@ -101,9 +101,6 @@ def load(_dir, _process=None, _format=None, _stream='stdout',
 
     # Create a DataFrame from the matches.
     df = pd.DataFrame(matches)
-    if _process and not df.empty:
-        df['res'] = df.resfile.apply(_process)
-        df = df.drop('resfile', axis=1)
 
     # Optionally try to convert string argument values to numeric types.
     if _infer_types:
@@ -111,6 +108,13 @@ def load(_dir, _process=None, _format=None, _stream='stdout',
         df.to_csv(buf)
         df = pd.read_csv(StringIO(buf.getvalue()), index_col=0)
 
+    # Open and process the results. This needs to happen after the type
+    # infererence phase since the processed results can be arbitrary
+    # Python objects and might not survive the round-trip.
+    if _process and not df.empty:
+        df['res'] = df.resfile.apply(_process)
+        df = df.drop('resfile', axis=1)
+
     return df
 
 def _parse_name(file, sep='\t'):