diff --git a/gobblin-runtime/src/main/java/org/apache/gobblin/runtime/spec_catalog/FlowCatalog.java b/gobblin-runtime/src/main/java/org/apache/gobblin/runtime/spec_catalog/FlowCatalog.java
index 8ac02145498..0a401f8b809 100644
--- a/gobblin-runtime/src/main/java/org/apache/gobblin/runtime/spec_catalog/FlowCatalog.java
+++ b/gobblin-runtime/src/main/java/org/apache/gobblin/runtime/spec_catalog/FlowCatalog.java
@@ -24,6 +24,7 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Iterator;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
@@ -97,8 +98,10 @@ public class FlowCatalog extends AbstractIdleService implements SpecCatalog, Mut
   @Getter
   protected final SpecStore specStore;
   // a map which keeps a handle of condition variables for each spec being added to the flow catalog
-  // to provide synchronization needed for flow specs
-  private final Map<String, Object> specSyncObjects = new HashMap<>();
+  // to provide synchronization needed for flow specs.
+  // Must be ConcurrentHashMap because onAddSpec is no longer synchronized (GOBBLIN-2257), so
+  // multiple updateOrAddSpecHelper calls can concurrently put/remove entries.
+  private final Map<String, Object> specSyncObjects = new ConcurrentHashMap<>();
 
   public FlowCatalog(Config config) {
     this(config, Optional.absent());
@@ -359,7 +362,7 @@ private Spec getSpecHelper(URI uri, ExponentialBackoff exponentialBackoff)
       if (exponentialBackoff.awaitNextRetryIfAvailable()) {
         return getSpecHelper(uri, exponentialBackoff);
       } else {
-        log.error(String.format("The URI %s discovered in SpecStore is missing in FlowCatalog" + ", suspecting current modification on SpecStore", uri), snfe);
+        log.warn(String.format("The URI %s discovered in SpecStore is missing in FlowCatalog" + ", suspecting current modification on SpecStore", uri), snfe);
       }
     }
     return spec;