diff --git a/src/main/java/net/openhft/chronicle/map/ChronicleMapBuilder.java b/src/main/java/net/openhft/chronicle/map/ChronicleMapBuilder.java
index cc0d6a88e..f700dcb42 100755
--- a/src/main/java/net/openhft/chronicle/map/ChronicleMapBuilder.java
+++ b/src/main/java/net/openhft/chronicle/map/ChronicleMapBuilder.java
@@ -147,10 +147,10 @@ public final class ChronicleMapBuilder<K, V> implements
     private long entriesPerSegment = -1L;
     private long actualChunksPerSegmentTier = -1L;
     private double averageKeySize = UNDEFINED_DOUBLE_CONFIG;
-    private K averageKey;
+    K averageKey;
     private K sampleKey;
     private double averageValueSize = UNDEFINED_DOUBLE_CONFIG;
-    private V averageValue;
+    V averageValue;
     private V sampleValue;
     private int actualChunkSize = 0;
     private int worstAlignment = -1;
diff --git a/src/test/java/net/openhft/chronicle/map/CHMUseCasesTest.java b/src/test/java/net/openhft/chronicle/map/CHMUseCasesTest.java
index 85c51ab3d..77d47c658 100644
--- a/src/test/java/net/openhft/chronicle/map/CHMUseCasesTest.java
+++ b/src/test/java/net/openhft/chronicle/map/CHMUseCasesTest.java
@@ -243,9 +243,9 @@ public class CHMUseCasesTest {
 
     private <X, Y> ChronicleMap<X, Y> newInstance(ChronicleMapBuilder<X, Y> builder) throws
             IOException {
-        if (!builder.constantlySizedKeys())
+        if (!builder.constantlySizedKeys() && builder.averageKey == null)
             builder.averageKeySize(20);
-        if (!builder.constantlySizedValues())
+        if (!builder.constantlySizedValues() && builder.averageValue == null)
             builder.averageValueSize(20);
         switch (typeOfMap) {
 
@@ -2597,6 +2597,8 @@ public class CHMUseCasesTest {
     public void testMapStringIntegerValueWithoutListMarshallers() throws IOException {
         ChronicleMapBuilder<String, Map<String, Integer>> builder = ChronicleMapBuilder
                 .of(String.class, (Class<Map<String, Integer>>) (Class) Map.class)
+                .averageKey("2")
+                .averageValue(mapOf("two", 2))
                 .entries(2);
         try (ChronicleMap<String, Map<String, Integer>> map = newInstance(builder)) {
             map.put("1", Collections.<String, Integer>emptyMap());