Index: oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/nodetype/write/NodeTypeTemplateImpl.java
===================================================================
--- oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/nodetype/write/NodeTypeTemplateImpl.java	(revision 1801467)
+++ oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/nodetype/write/NodeTypeTemplateImpl.java	(working copy)
@@ -25,6 +25,7 @@
 import static org.apache.jackrabbit.JcrConstants.JCR_PRIMARYTYPE;
 import static org.apache.jackrabbit.JcrConstants.JCR_PROPERTYDEFINITION;
 import static org.apache.jackrabbit.JcrConstants.JCR_SUPERTYPES;
+import static org.apache.jackrabbit.JcrConstants.NT_BASE;
 import static org.apache.jackrabbit.JcrConstants.NT_CHILDNODEDEFINITION;
 import static org.apache.jackrabbit.JcrConstants.NT_NODETYPE;
 import static org.apache.jackrabbit.JcrConstants.NT_PROPERTYDEFINITION;
@@ -146,12 +147,20 @@
 
         type.setProperty(JCR_NODETYPENAME, oakName, Type.NAME);
 
-        if (superTypeOakNames.length > 0) {
+        if (oakName.equals(NT_BASE)) {
+            // nt:base is the only node type without supertypes
+            // -> JCR 2.0 specification 3.7.10.1
+            type.removeProperty(JCR_SUPERTYPES);
+        } else if (superTypeOakNames.length > 0) {
             type.setProperty(
                     JCR_SUPERTYPES,
                     Arrays.asList(superTypeOakNames), Type.NAMES);
-        } else {
-            type.removeProperty(JCR_SUPERTYPES);
+        } else if (!isMixin()) {
+            // primary node types must at least be a subtype of nt:base
+            // -> JCR 2.0 specification 3.7.6
+            type.setProperty(
+                    JCR_SUPERTYPES,
+                    Lists.newArrayList(NT_BASE), Type.NAMES);
         }
 
         type.setProperty(JCR_IS_ABSTRACT, isAbstract);
Index: oak-core/src/test/java/org/apache/jackrabbit/oak/plugins/nodetype/write/NodeTypeRegistryTest.java
===================================================================
--- oak-core/src/test/java/org/apache/jackrabbit/oak/plugins/nodetype/write/NodeTypeRegistryTest.java	(revision 1801476)
+++ oak-core/src/test/java/org/apache/jackrabbit/oak/plugins/nodetype/write/NodeTypeRegistryTest.java	(working copy)
@@ -75,7 +75,6 @@
 import org.apache.jackrabbit.oak.plugins.tree.TreeUtil;
 import org.junit.After;
 import org.junit.Before;
-import org.junit.Ignore;
 import org.junit.Test;
 
 import static org.junit.Assert.assertFalse;
@@ -172,7 +171,6 @@
 
     }
 
-    @Ignore("OAK-6440")
     @Test
     public void registerNodeType() throws Exception {
         registerNodeType(root, "oak6440-1.cnd");