diff --git a/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/refactoring/includes/BindingClassifierTest.java b/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/refactoring/includes/BindingClassifierTest.java
index 4c63997f3d3..c81e0433be6 100644
--- a/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/refactoring/includes/BindingClassifierTest.java
+++ b/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/refactoring/includes/BindingClassifierTest.java
@@ -411,6 +411,17 @@ public class BindingClassifierTest extends OneSourceMultipleHeadersTestCase {
 		assertDeclared();
 	}
 
+	//	class Base {};
+
+	//	class Derived : public Base {
+	//	public:
+	//	  Derived();
+	//	};
+	public void testBaseClause_421398() throws Exception {
+		assertDefined("Base");
+		assertDeclared();
+	}
+
 	//	struct A {};
 	//	template<typename T> struct B {};
 	//	template<typename T, typename U = B<T>> struct C {};
diff --git a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/refactoring/includes/BindingClassifier.java b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/refactoring/includes/BindingClassifier.java
index ed6394a0d50..e41b14ffdfb 100644
--- a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/refactoring/includes/BindingClassifier.java
+++ b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/refactoring/includes/BindingClassifier.java
@@ -516,7 +516,7 @@ public class BindingClassifier {
 				// Record the fact that we also have a definition of the typedef's target type.
 				markAsDefined((IBinding) type);
 			}
-		} else if (binding instanceof ICPPClassType) {
+		} else if (binding instanceof ICPPClassType && fAst.getDefinitionsInAST(binding).length == 0) {
 			// The header that defines a class must provide definitions of all its base classes.
 			ICPPClassType[] bases = ClassTypeHelper.getAllBases((ICPPClassType) binding, fAst);
 			for (ICPPClassType base : bases) {