diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/index/CIndex.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/index/CIndex.java
index 486fa0b16c4..a9d588bbdc5 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/index/CIndex.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/index/CIndex.java
@@ -560,7 +560,7 @@ public class CIndex implements IIndex {
 			// if non-empty (non-c) results are returned by a fragment
 			return fCF;
 		}
-		throw new CompositingNotImplementedError();
+		throw new CompositingNotImplementedError("Compositing not implemented for linkage ID " + linkageID);  //$NON-NLS-1$
 	}
 
 	private IndexFilter retargetFilter(final ILinkage linkage, final IndexFilter filter) {