diff --git a/hgext/rebase.py b/hgext/rebase.py
--- a/hgext/rebase.py
+++ b/hgext/rebase.py
@@ -274,8 +274,12 @@ def rebase(ui, repo, **opts):
                                 "can't compute rebase set\n"))
                     return 1
                 commonanc = repo.revs('ancestor(%ld, %d)', base, dest).first()
-                rebaseset = repo.revs('(%d::(%ld) - %d)::',
-                                      commonanc, base, commonanc)
+                if commonanc is not None:
+                    rebaseset = repo.revs('(%d::(%ld) - %d)::',
+                                          commonanc, base, commonanc)
+                else:
+                    rebaseset = []
+
                 if not rebaseset:
                     # transform to list because smartsets are not comparable to
                     # lists. This should be improved to honor lazyness of
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
@@ -468,3 +468,17 @@ Test --tool parameter:
   [255]
 
   $ cd ..
+
+No common ancestor
+
+  $ hg init separaterepo
+  $ cd separaterepo
+  $ touch a
+  $ hg commit -Aqm a
+  $ hg up -q null
+  $ touch b
+  $ hg commit -Aqm b
+  $ hg rebase -d 0
+  nothing to rebase from d7486e00c6f1 to 3903775176ed
+  [1]
+  $ cd ..