diff --git a/packages/mongo-livedata/polling_observe_driver.js b/packages/mongo-livedata/polling_observe_driver.js
index c1c700d0c19..9bfca7ec44a 100644
--- a/packages/mongo-livedata/polling_observe_driver.js
+++ b/packages/mongo-livedata/polling_observe_driver.js
@@ -126,10 +126,11 @@ _.extend(PollingObserveDriver.prototype, {
     --self._pollsScheduledButNotStarted;
 
     var first = false;
-    if (!self._results) {
+    var oldResults = self._results;
+    if (!oldResults) {
       first = true;
       // XXX maybe use OrderedDict instead?
-      self._results = self._ordered ? [] : new LocalCollection._IdMap;
+      oldResults = self._ordered ? [] : new LocalCollection._IdMap;
     }
 
     self._testOnlyPollCallback && self._testOnlyPollCallback();
@@ -138,25 +139,39 @@ _.extend(PollingObserveDriver.prototype, {
     var writesForCycle = self._pendingWrites;
     self._pendingWrites = [];
 
-    // Get the new query results. (These calls can yield.)
-    if (!first)
-      self._synchronousCursor.rewind();
-    var newResults = self._synchronousCursor.getRawObjects(self._ordered);
-    var oldResults = self._results;
+    // Always rewind the cursor; it's a no-op the first time, but better safe
+    // than sorry (eg, if the first call to getRawObjects throws, the cursor
+    // needs rewinding even though 'first' is true).
+    self._synchronousCursor.rewind();
+
+    // Get the new query results. (This yields.)
+    try {
+      var newResults = self._synchronousCursor.getRawObjects(self._ordered);
+    } catch (e) {
+      // getRawObjects can throw if we're having trouble talking to the
+      // database.  That's fine --- we will repoll later anyway. But we should
+      // make sure not to lose track of this cycle's writes.
+      Array.prototype.push.apply(self._pendingWrites, writesForCycle);
+      throw e;
+    }
 
-    // Run diffs. (This can yield too.)
+    // Run diffs.
     if (!self._stopped) {
       LocalCollection._diffQueryChanges(
         self._ordered, oldResults, newResults, self._multiplexer);
     }
 
-    // Replace self._results atomically.
-    self._results = newResults;
-
-    // Signals the multiplexer to call all initial adds.
+    // Signals the multiplexer to allow all observeChanges calls that share this
+    // multiplexer to return. (This happens asynchronously, via the
+    // multiplexer's queue.)
     if (first)
       self._multiplexer.ready();
 
+    // Replace self._results atomically.  (This assignment is what makes `first`
+    // stay through on the next cycle, so we've waited until after we've
+    // committed to ready-ing the multiplexer.)
+    self._results = newResults;
+
     // Once the ObserveMultiplexer has processed everything we've done in this
     // round, mark all the writes which existed before this call as
     // commmitted. (If new writes have shown up in the meantime, there'll