diff --git a/src/applications/diffusion/query/lowlevel/DiffusionLowLevelResolveRefsQuery.php b/src/applications/diffusion/query/lowlevel/DiffusionLowLevelResolveRefsQuery.php
--- a/src/applications/diffusion/query/lowlevel/DiffusionLowLevelResolveRefsQuery.php
+++ b/src/applications/diffusion/query/lowlevel/DiffusionLowLevelResolveRefsQuery.php
@@ -204,6 +204,10 @@
           // unclear how to best do that. For now, treat it as a miss instead.
           continue;
         }
+        if (preg_match('/unknown revision/', $ex->getStdErr())) {
+          // No matches for this ref.
+          continue;
+        }
         throw $ex;
       }
 
diff --git a/src/applications/diffusion/request/DiffusionRequest.php b/src/applications/diffusion/request/DiffusionRequest.php
--- a/src/applications/diffusion/request/DiffusionRequest.php
+++ b/src/applications/diffusion/request/DiffusionRequest.php
@@ -755,7 +755,12 @@
 
   public function getRefAlternatives() {
     // Make sure we've resolved the reference into a stable commit first.
-    $this->getStableCommit();
+    try {
+      $this->getStableCommit();
+    } catch (DiffusionRefNotFoundException $ex) {
+      // If we have a bad reference, just return the empty set of
+      // alternatives.
+    }
     return $this->refAlternatives;
   }