diff --git a/packages/mongo-livedata/oplog_observe_driver.js b/packages/mongo-livedata/oplog_observe_driver.js
index 8400373390..5fb94ec4b1 100644
--- a/packages/mongo-livedata/oplog_observe_driver.js
+++ b/packages/mongo-livedata/oplog_observe_driver.js
@@ -287,15 +287,11 @@ _.extend(OplogObserveDriver.prototype, {
       self._removeBuffered(id);
     }
   },
-  _handleDoc: function (id, newDoc, mustMatchNow) {
+  _handleDoc: function (id, newDoc) {
     var self = this;
     newDoc = _.clone(newDoc);
 
     var matchesNow = newDoc && self._matcher.documentMatches(newDoc).result;
-    if (mustMatchNow && !matchesNow) {
-      throw Error("expected " + EJSON.stringify(newDoc) + " to match "
-                  + EJSON.stringify(self._cursorDescription));
-    }
 
     var publishedBefore = self._published.has(id);
     var bufferedBefore = self._limit && self._unpublishedBuffer.has(id);
@@ -678,9 +674,18 @@ _.extend(OplogObserveDriver.prototype, {
     // If self has a buffer and limit, the new fetched result will be
     // limited correctly as the query has sort specifier.
     newResults.forEach(function (doc, id) {
-      // "true" here means to throw if we think this doc doesn't match the
-      // selector.
-      self._handleDoc(id, doc, true);
+      self._handleDoc(id, doc);
+    });
+
+    // Sanity-check that everything we tried to put into _published ended up
+    // there.
+    // XXX if this is slow, remove it later
+    if (self._published.size() !== newResults.size()) {
+      throw Error("failed to copy newResults into _published!");
+    }
+    self._published.forEach(function (doc, id) {
+      if (!newResults.has(id))
+        throw Error("_published has a doc that newResults doesn't; " + id);
     });
 
     // Finally, replace the buffer