diff --git a/heudiconv/main.py b/heudiconv/main.py
index 5c6f37d5..29465760 100644
--- a/heudiconv/main.py
+++ b/heudiconv/main.py
@@ -83,7 +83,7 @@ def process_extra_commands(outdir, command, files, dicom_dir_template,
         heuristic_ls = getattr(heuristic, 'ls', None)
         for f in files:
             study_sessions = get_study_sessions(
-                dicom_dir_template, [f], heuristic, outdir,
+                [f], dicom_dir_template, heuristic, outdir,
                 session, subjs, grouping=grouping)
             print(f)
             for study_session, sequences in study_sessions.items():
@@ -324,7 +324,7 @@ def workflow(*, dicom_dir_template=None, files=None, subjs=None,
 
     heuristic = load_heuristic(heuristic)
 
-    study_sessions = get_study_sessions(dicom_dir_template, files,
+    study_sessions = get_study_sessions(files, dicom_dir_template,
                                         heuristic, outdir, session,
                                         subjs, grouping=grouping)
 
diff --git a/heudiconv/parser.py b/heudiconv/parser.py
index 3db1fc2c..89e3b8a7 100644
--- a/heudiconv/parser.py
+++ b/heudiconv/parser.py
@@ -113,8 +113,18 @@ def get_extracted_dicoms(fl):
 
     return sessions.items()
 
+from fscacher import PersistentCache
+from ._version import __version__
 
-def get_study_sessions(dicom_dir_template, files_opt, heuristic, outdir,
+study_sessions_cache =  PersistentCache(
+    name="heudiconv-study-sessions",
+    tokens=[__version__],
+    envvar="HEUDICONV_CACHE",
+)
+
+
+@study_sessions_cache.memoize_paths
+def get_study_sessions(files_opt, dicom_dir_template, heuristic, outdir,
                        session, sids, grouping='studyUID'):
     """Given options from cmdline sort files or dicom seqinfos into
     study_sessions which put together files for a single session of a subject