diff --git a/solr/core/src/java/org/apache/solr/cloud/ZkController.java b/solr/core/src/java/org/apache/solr/cloud/ZkController.java
index 053599818fd..185a50ccb24 100644
--- a/solr/core/src/java/org/apache/solr/cloud/ZkController.java
+++ b/solr/core/src/java/org/apache/solr/cloud/ZkController.java
@@ -31,6 +31,7 @@ import java.util.Enumeration;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Properties;
 import java.util.Set;
@@ -872,7 +873,7 @@ public final class ZkController {
             .getCoreUrl();
         
         if (tries % 30 == 0) {
-          String warnMsg = String.format("Still seeing conflicting information about the leader "
+          String warnMsg = String.format(Locale.ENGLISH, "Still seeing conflicting information about the leader "
               + "of shard %s for collection %s after %d seconds; our state says %s, but ZooKeeper says %s",
               cloudDesc.getShardId(), collection, tries, clusterStateLeaderUrl, leaderUrl);
           log.warn(warnMsg);