diff --git a/20-trench-map/code.scm b/20-trench-map/code.scm
index 6d21a53..3427a5d 100644
--- a/20-trench-map/code.scm
+++ b/20-trench-map/code.scm
@@ -67,10 +67,10 @@
 	  (image (begin
 		   (get-line file) ; skip empty line
 		   (file->matrix file)))]
-      (let [(enhanced (enhance image enhancer 2))]
+      (let [(enhanced-2 (enhance image enhancer 2))]
 	(printf "part 1:~% Lit pixels after enhancing twice: ~a~%"
-		(matrix-sum enhanced)))
-      (let [(enhanced (enhance image enhancer 50))]
-	(printf "part 2:~% Lit pixels after enhancing fifty times: ~a~%"
-		(matrix-sum enhanced))))))
+		(matrix-sum enhanced-2))
+	(let [(enhanced-50 (enhance enhanced-2 enhancer 48))]
+	  (printf "part 2:~% Lit pixels after enhancing fifty times: ~a~%"
+		  (matrix-sum enhanced-50)))))))