diff --git a/scheme/opt/usage.scm b/scheme/opt/usage.scm
index 397777f..49de9c2 100644
--- a/scheme/opt/usage.scm
+++ b/scheme/opt/usage.scm
@@ -189,6 +189,10 @@
 	     free
 	     usages)))
 
+(define-usage-analyzer 'flat-lambda #f
+  (lambda (node free usages)
+    (error "Inliner applied on flat lambda, please swap OPTIMIZE clauses")))
+
 ;--------------------
 ; Usage records record the number of times that a variable is referenced, set!,
 ; and called.