diff --git a/src/main/java/com/fasterxml/jackson/databind/ser/SerializerCache.java b/src/main/java/com/fasterxml/jackson/databind/ser/SerializerCache.java
index f763372f68..73f66e5784 100644
--- a/src/main/java/com/fasterxml/jackson/databind/ser/SerializerCache.java
+++ b/src/main/java/com/fasterxml/jackson/databind/ser/SerializerCache.java
@@ -217,5 +217,6 @@ public void addAndResolveNonTypedSerializer(Class<?> rawType, JavaType fullType,
      */
     public synchronized void flush() {
         _sharedMap.clear();
+        _readOnlyMap.set(null);
     }
 }