diff --git a/hgext3rd/treedirstate.py b/hgext3rd/treedirstate.py
--- a/hgext3rd/treedirstate.py
+++ b/hgext3rd/treedirstate.py
@@ -530,6 +530,15 @@
 def istreedirstate(repo):
     return 'treedirstate' in getattr(repo, 'requirements', set())
 
+def activealternativedirstates(repo):
+    """
+    Returns a set containing the names of any alternative dirstate
+    implementations in use.
+    """
+    alternatives = {'eden', 'sqldirstate'}
+    requirements = getattr(repo, 'requirements', set())
+    return alternatives & requirements
+
 def newtree(opener):
     while True:
         treeid = ''.join([random.choice(string.digits) for _c in range(8)])
@@ -551,6 +560,10 @@
 def upgrade(ui, repo):
     if istreedirstate(repo):
         raise error.Abort('repo already has treedirstate')
+    alternatives = activealternativedirstates(repo)
+    if alternatives:
+        raise error.Abort('repo has alternative dirstate active: %s'
+                          % ', '.join(alternatives))
     with repo.wlock():
         newmap = treedirstatemap(ui, repo.dirstate._opener, repo.root,
                                  importmap=repo.dirstate._map)
@@ -687,7 +700,7 @@
         ui.status(_('disabling treedirstate...\n'))
         downgrade(ui, repo)
     elif (ui.configbool('treedirstate', 'upgradeonpull') and
-            not istreedirstate(repo)):
+            not istreedirstate(repo) and not activealternativedirstates(repo)):
         ui.status(_('migrating your repo to treedirstate which will make your '
                     'hg commands faster...\n'))
         upgrade(ui, repo)
diff --git a/tests/test-treedirstate.t b/tests/test-treedirstate.t
--- a/tests/test-treedirstate.t
+++ b/tests/test-treedirstate.t
@@ -133,7 +133,7 @@
   .hg/dirstate.tree.* (glob)
   .hg/dirstate.tree.* (glob)
 
-Test downgrade and upgrade on pull
+Test downgrade on pull
 
   $ for f in 1 2 3 4 5 ; do mkdir dir$f ; echo $f > dir$f/file$f ; hg add dir$f/file$f ; done
   $ echo x > a
@@ -172,6 +172,29 @@
   a   0         -1 * newfile (glob)
   $ grep treedirstate .hg/requires
   [1]
+
+Test upgrade on pull with conflicting dirstate reimplementation
+
+  $ cat > $TESTTMP/fakesqldirstate.py << EOF
+  > from mercurial import localrepo
+  > def featuresetup(ui, supported):
+  >     supported |= {'sqldirstate'}
+  > def extsetup(ui):
+  >     localrepo.localrepository.featuresetupfuncs.add(featuresetup)
+  > EOF
+  $ cp .hg/requires .hg/requires.test-backup
+  $ echo sqldirstate >> .hg/requires
+  $ hg pull --config treedirstate.upgradeonpull=true --config extensions.fakesqldirstate=$TESTTMP/fakesqldirstate.py
+  pulling from $TESTTMP/repo (glob)
+  searching for changes
+  no changes found
+  $ hg debugtreedirstate on --config extensions.fakesqldirstate=$TESTTMP/fakesqldirstate.py
+  abort: repo has alternative dirstate active: sqldirstate
+  [255]
+  $ mv -f .hg/requires.test-backup .hg/requires
+
+Test upgrade on pull
+
   $ hg pull --config treedirstate.upgradeonpull=true
   migrating your repo to treedirstate which will make your hg commands faster...
   pulling from $TESTTMP/repo (glob)