diff --git a/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/mongo/replica/ReplicaSetInfo.java b/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/mongo/replica/ReplicaSetInfo.java
index 2a7e6c5..a347746 100644
--- a/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/mongo/replica/ReplicaSetInfo.java
+++ b/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/mongo/replica/ReplicaSetInfo.java
@@ -250,18 +250,22 @@ public class ReplicaSetInfo implements Runnable {
             }
         }
 
+        Set<String> hostsToCheck = new HashSet<String>();
         if (secondaries.isEmpty()) {
             LOG.debug("No secondaries found: {}", members);
             unknownState = true;
+        } else {
+            hostsToCheck.addAll(secondaries);
         }
 
         if (primary == null) {
             LOG.debug("No primary found: {}", members);
             unknownState = true;
+        } else {
+            hostsToCheck.add(primary);
         }
 
         Map<String, Timestamped<RevisionVector>> vectors = null;
-        Set<String> hostsToCheck = union(secondaries, of(primary));
         if (!unknownState) {
             vectors = getRootRevisions(hostsToCheck);
             if (vectors.containsValue(null)) {