--- a/mercurial/repair.py	Mon Jun 19 13:13:28 2017 -0700
+++ b/mercurial/repair.py	Mon Jun 19 13:18:00 2017 -0700
@@ -79,6 +79,9 @@
     # This function requires the caller to lock the repo, but it operates
     # within a transaction of its own, and thus requires there to be no current
     # transaction when it is called.
+    if repo.currenttransaction() is not None:
+        raise error.ProgrammingError('cannot strip from inside a transaction')
+
     # Simple way to maintain backwards compatibility for this
     # argument.
     if backup in ['none', 'strip']:
@@ -168,9 +171,6 @@
 
     mfst = repo.manifestlog._revlog
 
-    if repo.currenttransaction() is not None:
-        raise error.ProgrammingError('cannot strip from inside a transaction')
-
     try:
         with repo.transaction("strip") as tr:
             offset = len(tr.entries)