diff --git a/modules/lang-painless/src/main/java/org/elasticsearch/painless/ScriptClassInfo.java b/modules/lang-painless/src/main/java/org/elasticsearch/painless/ScriptClassInfo.java
index 345db46f887..7de8353194d 100644
--- a/modules/lang-painless/src/main/java/org/elasticsearch/painless/ScriptClassInfo.java
+++ b/modules/lang-painless/src/main/java/org/elasticsearch/painless/ScriptClassInfo.java
@@ -21,6 +21,7 @@ package org.elasticsearch.painless;
 
 import org.elasticsearch.painless.lookup.PainlessLookup;
 import org.elasticsearch.painless.lookup.PainlessLookupUtility;
+import org.elasticsearch.painless.lookup.def;
 
 import java.lang.invoke.MethodType;
 import java.lang.reflect.Field;
@@ -190,7 +191,7 @@ public class ScriptClassInfo {
             componentType = componentType.getComponentType();
         }
 
-        if (painlessLookup.lookupPainlessClass(componentType) == null) {
+        if (componentType != def.class && painlessLookup.lookupPainlessClass(componentType) == null) {
             throw new IllegalArgumentException(unknownErrorMessageSource.apply(componentType));
         }
 
diff --git a/modules/lang-painless/src/main/java/org/elasticsearch/painless/lookup/PainlessLookup.java b/modules/lang-painless/src/main/java/org/elasticsearch/painless/lookup/PainlessLookup.java
index 16b8ac14f14..55855a3cb1e 100644
--- a/modules/lang-painless/src/main/java/org/elasticsearch/painless/lookup/PainlessLookup.java
+++ b/modules/lang-painless/src/main/java/org/elasticsearch/painless/lookup/PainlessLookup.java
@@ -26,6 +26,7 @@ import java.util.Objects;
 import java.util.Set;
 import java.util.function.Function;
 
+import static org.elasticsearch.painless.lookup.PainlessLookupUtility.DEF_CLASS_NAME;
 import static org.elasticsearch.painless.lookup.PainlessLookupUtility.buildPainlessConstructorKey;
 import static org.elasticsearch.painless.lookup.PainlessLookupUtility.buildPainlessFieldKey;
 import static org.elasticsearch.painless.lookup.PainlessLookupUtility.buildPainlessMethodKey;
@@ -47,7 +48,7 @@ public final class PainlessLookup {
     public boolean isValidCanonicalClassName(String canonicalClassName) {
         Objects.requireNonNull(canonicalClassName);
 
-        return canonicalClassNamesToClasses.containsKey(canonicalClassName);
+        return DEF_CLASS_NAME.equals(canonicalClassName) || canonicalClassNamesToClasses.containsKey(canonicalClassName);
     }
 
     public Class<?> canonicalTypeNameToType(String canonicalTypeName) {
diff --git a/modules/lang-painless/src/main/java/org/elasticsearch/painless/lookup/PainlessLookupBuilder.java b/modules/lang-painless/src/main/java/org/elasticsearch/painless/lookup/PainlessLookupBuilder.java
index e644453a4c1..c8353b54c9f 100644
--- a/modules/lang-painless/src/main/java/org/elasticsearch/painless/lookup/PainlessLookupBuilder.java
+++ b/modules/lang-painless/src/main/java/org/elasticsearch/painless/lookup/PainlessLookupBuilder.java
@@ -211,9 +211,6 @@ public final class PainlessLookupBuilder {
     public PainlessLookupBuilder() {
         canonicalClassNamesToClasses = new HashMap<>();
         classesToPainlessClassBuilders = new HashMap<>();
-
-        canonicalClassNamesToClasses.put(DEF_CLASS_NAME, def.class);
-        classesToPainlessClassBuilders.put(def.class, new PainlessClassBuilder());
     }
 
     private Class<?> canonicalTypeNameToType(String canonicalTypeName) {
@@ -225,7 +222,7 @@ public final class PainlessLookupBuilder {
             type = type.getComponentType();
         }
 
-        return classesToPainlessClassBuilders.containsKey(type);
+        return type == def.class || classesToPainlessClassBuilders.containsKey(type);
     }
 
     public void addPainlessClass(ClassLoader classLoader, String javaClassName, boolean importClassName) {
diff --git a/modules/lang-painless/src/main/java/org/elasticsearch/painless/lookup/PainlessLookupUtility.java b/modules/lang-painless/src/main/java/org/elasticsearch/painless/lookup/PainlessLookupUtility.java
index f2eb4345169..71cacab9eba 100644
--- a/modules/lang-painless/src/main/java/org/elasticsearch/painless/lookup/PainlessLookupUtility.java
+++ b/modules/lang-painless/src/main/java/org/elasticsearch/painless/lookup/PainlessLookupUtility.java
@@ -82,7 +82,7 @@ public final class PainlessLookupUtility {
         Objects.requireNonNull(canonicalTypeName);
         Objects.requireNonNull(canonicalClassNamesToClasses);
 
-        Class<?> type = canonicalClassNamesToClasses.get(canonicalTypeName);
+        Class<?> type = DEF_CLASS_NAME.equals(canonicalTypeName) ? def.class : canonicalClassNamesToClasses.get(canonicalTypeName);
 
         if (type != null) {
             return type;
@@ -105,7 +105,7 @@ public final class PainlessLookupUtility {
             }
 
             canonicalTypeName = canonicalTypeName.substring(0, canonicalTypeName.indexOf('['));
-            type = canonicalClassNamesToClasses.get(canonicalTypeName);
+            type = DEF_CLASS_NAME.equals(canonicalTypeName) ? def.class : canonicalClassNamesToClasses.get(canonicalTypeName);
 
             if (type != null) {
                 char arrayBraces[] = new char[arrayDimensions];