diff --git a/src/main/java/net/openhft/chronicle/map/ChronicleMapBuilder.java b/src/main/java/net/openhft/chronicle/map/ChronicleMapBuilder.java
index 0f68572fa..523de2a4d 100644
--- a/src/main/java/net/openhft/chronicle/map/ChronicleMapBuilder.java
+++ b/src/main/java/net/openhft/chronicle/map/ChronicleMapBuilder.java
@@ -53,11 +53,11 @@ public final class ChronicleMapBuilder<K, V> implements ChronicleMapBuilderI<K,
         if (valueClass.isEnum())
             return new ChronicleMapBuilder<K, V>(OnHeapUpdatableChronicleMapBuilder.of(keyClass, valueClass));
 
-        if (keyClass.isInterface() && keyClass != CharSequence.class) {
+        if (keyClass.isInterface() && !builtInType(keyClass)) {
             keyClass = DataValueClasses.directClassFor(keyClass);
         }
 
-        if ((valueClass.isInterface() && valueClass != CharSequence.class)) {
+        if ((valueClass.isInterface() && !builtInType(valueClass))) {
             valueClass = DataValueClasses.directClassFor(valueClass);
         } else if (!offHeapReference(valueClass)) {
             return new ChronicleMapBuilder<K, V>(OnHeapUpdatableChronicleMapBuilder.of(keyClass, valueClass));
@@ -67,6 +67,10 @@ public final class ChronicleMapBuilder<K, V> implements ChronicleMapBuilderI<K,
         return new ChronicleMapBuilder<K, V>(kvOffHeapUpdatableChronicleMapBuilder);
     }
 
+    static boolean builtInType(Class clazz) {
+        return clazz.getClassLoader() == Class.class.getClassLoader();
+    }
+
     ChronicleMapBuilder(ChronicleMapBuilderI<K, V> delegate) {
         this.delegate = delegate;
     }