diff --git a/include/noun/trace.h b/include/noun/trace.h
index e629639c8..5b847f521 100644
--- a/include/noun/trace.h
+++ b/include/noun/trace.h
@@ -6,7 +6,7 @@
   **/
     /* U3_CPU_DEBUG: activate profiling.
     */
-#     define U3_CPU_DEBUG
+#     undef U3_CPU_DEBUG
 
   /** Data structures.
   **/