diff --git a/collects/macro-debugger/syntax-browser/text.rkt b/collects/macro-debugger/syntax-browser/text.rkt
index 8cbcf9c..a5b546a 100644
--- a/collects/macro-debugger/syntax-browser/text.rkt
+++ b/collects/macro-debugger/syntax-browser/text.rkt
@@ -105,7 +105,7 @@
              invalidate-bitmap-cache)
 
     ;; interval-map of Drawings
-    (define drawings-list (make-numeric-interval-map))
+    (define drawings-list (make-interval-map))
 
     (field [hover-position #f])