diff --git a/anki/sync.py b/anki/sync.py
index 53c937f01..d0980728a 100644
--- a/anki/sync.py
+++ b/anki/sync.py
@@ -107,6 +107,9 @@ class Syncer(object):
         elif lscm != rscm:
             return "fullSync"
         self.lnewer = self.lmod > self.rmod
+        # step 1.5: check collection is valid
+        if not self.col.basicCheck():
+            return "basicCheckFailed"
         # step 2: deletions
         runHook("sync", "meta")
         lrem = self.removed()
@@ -182,12 +185,8 @@ class Syncer(object):
         self.prepareToChunk()
 
     def sanityCheck(self):
-        if self.col.db.scalar("""
-select count() from cards where nid not in (select id from notes)"""):
-            return "missing notes"
-        if self.col.db.scalar("""
-select count() from notes where id not in (select distinct nid from cards)"""):
-            return "missing cards"
+        if not self.col.basicCheck():
+            return "failed basic check"
         for t in "cards", "notes", "revlog", "graves":
             if self.col.db.scalar(
                 "select count() from %s where usn = -1" % t):
diff --git a/aqt/sync.py b/aqt/sync.py
index fdd500288..87946f7c2 100644
--- a/aqt/sync.py
+++ b/aqt/sync.py
@@ -114,6 +114,8 @@ Please visit AnkiWeb, upgrade your deck, then try again."""))
                      self._rewriteError(args[0]))
         elif evt == "clockOff":
             self._clockOff()
+        elif evt == "basicCheckFailed":
+            self._basicCheckFailed()
         elif evt == "noChanges":
             pass
         elif evt == "fullSync":
@@ -237,6 +239,11 @@ automatically."""),
 Syncing requires the clock on your computer to be set correctly. Please \
 fix the clock and try again."""))
 
+    def _basicCheckFailed(self):
+        showWarning(_("""\
+Your collection is in an inconsistent state. Please run Tools>\
+Maintenance>Check Database."""))
+
     def badUserPass(self):
         aqt.preferences.Preferences(self, self.pm.profile).dialog.tabWidget.\
                                          setCurrentIndex(1)
@@ -330,6 +337,8 @@ class SyncThread(QThread):
             return self.fireEvent("badAuth")
         elif ret == "clockOff":
             return self.fireEvent("clockOff")
+        elif ret == "basicCheckFailed":
+            return self.fireEvent("basicCheckFailed")
         # note mediaUSN for later
         self.mediaUsn = self.client.mediaUsn
         # full sync?