diff --git a/hgext/rebase.py b/hgext/rebase.py
--- a/hgext/rebase.py
+++ b/hgext/rebase.py
@@ -712,8 +712,8 @@ def defineparents(repo, rev, target, sta
     repo.ui.debug(" future parents are %d and %d\n" %
                             (repo[p1].rev(), repo[p2].rev()))
 
-    if rev == min(state):
-        # Case (1) initial changeset of a non-detaching rebase.
+    if not any(p.rev() in state for p in parents):
+        # Case (1) root changeset of a non-detaching rebase set.
         # Let the merge mechanism find the base itself.
         base = None
     elif not repo[rev].p2():
diff --git a/tests/test-rebase-parameters.t b/tests/test-rebase-parameters.t
--- a/tests/test-rebase-parameters.t
+++ b/tests/test-rebase-parameters.t
@@ -412,6 +412,16 @@ Specify only revs (from 2 onto 8)
   
   $ cd ..
 
+Rebasing both a single revision and a merge in one command
+
+  $ hg clone -q -u . a aX
+  $ cd aX
+  $ hg rebase -r 3 -r 6
+  rebasing 3:32af7686d403 "D"
+  rebasing 6:eea13746799a "G"
+  saved backup bundle to $TESTTMP/aX/.hg/strip-backup/eea13746799a-ad273fd6-backup.hg (glob)
+  $ cd ..
+
 Test --tool parameter:
 
   $ hg init b