diff --git a/plugins/org.eclipse.xtext/src/org/eclipse/xtext/naming/QualifiedName.java b/plugins/org.eclipse.xtext/src/org/eclipse/xtext/naming/QualifiedName.java
index b207abb47..55075317f 100644
--- a/plugins/org.eclipse.xtext/src/org/eclipse/xtext/naming/QualifiedName.java
+++ b/plugins/org.eclipse.xtext/src/org/eclipse/xtext/naming/QualifiedName.java
@@ -95,6 +95,9 @@ public class QualifiedName implements Comparable<QualifiedName> {
 	}
 
 	public QualifiedName append(String segment) {
+		if (segment == null) {
+			throw new IllegalArgumentException("Segment cannot be null");
+		}
 		String[] newSegments = new String[getSegmentCount() + 1];
 		System.arraycopy(segments, 0, newSegments, 0, segments.length);
 		newSegments[segments.length] = segment;
diff --git a/tests/org.eclipse.xtext.tests/src/org/eclipse/xtext/naming/QualifiedNameTest.java b/tests/org.eclipse.xtext.tests/src/org/eclipse/xtext/naming/QualifiedNameTest.java
index 49772b0bd..1ddf2f7a7 100644
--- a/tests/org.eclipse.xtext.tests/src/org/eclipse/xtext/naming/QualifiedNameTest.java
+++ b/tests/org.eclipse.xtext.tests/src/org/eclipse/xtext/naming/QualifiedNameTest.java
@@ -25,6 +25,13 @@ public class QualifiedNameTest extends TestCase {
 			fail("Exception expected");
 		} catch(IllegalArgumentException e) {}
 	}
+	
+	public void testAppendNull() {
+		try {
+			QualifiedName.create().append((String) null);
+			fail("Exception expected");
+		} catch (IllegalArgumentException e) {}
+	}
 
 	public void testSegments() {
 		QualifiedName qn = QualifiedName.create("foo", "bar", "baz");