diff --git a/compiler/optimizing/graph_checker.cc b/compiler/optimizing/graph_checker.cc
index 35c5269..4ebb136 100644
--- a/compiler/optimizing/graph_checker.cc
+++ b/compiler/optimizing/graph_checker.cc
@@ -153,8 +153,9 @@
         ? use->GetBlock()->GetPhis()
         : use->GetBlock()->GetInstructions();
     if (!list.Contains(use)) {
-      AddError(StringPrintf("User %d of instruction %d is not defined "
+      AddError(StringPrintf("User %s:%d of instruction %d is not defined "
                             "in a basic block of the control-flow graph.",
+                            use->DebugName(),
                             use->GetId(),
                             instruction->GetId()));
     }