Fix for 18604.
diff --git a/bundles/org.eclipse.core.runtime/src/org/eclipse/core/runtime/QualifiedName.java b/bundles/org.eclipse.core.runtime/src/org/eclipse/core/runtime/QualifiedName.java
index 1ac5d7b..c9cafab 100644
--- a/bundles/org.eclipse.core.runtime/src/org/eclipse/core/runtime/QualifiedName.java
+++ b/bundles/org.eclipse.core.runtime/src/org/eclipse/core/runtime/QualifiedName.java
@@ -103,6 +103,6 @@
  * debug purposes only.
  */
 public String toString() {
-	return "QualifiedName(" + (getQualifier() == null ? "null" : getQualifier()) + ',' + getLocalName() + ')'; //$NON-NLS-1$ //$NON-NLS-2$
+	return (getQualifier() == null ? "" : getQualifier() + ':') + getLocalName(); //$NON-NLS-1$
 }
 }