diff --git a/ice-9/debug.scm b/ice-9/debug.scm
index 1fdc212b7..1edd25af8 100644
--- a/ice-9/debug.scm
+++ b/ice-9/debug.scm
@@ -111,6 +111,14 @@
 
 (define-all)
 
+
+;;; {Misc}
+;;;
+(define-public (frame-number->index n)
+  (if (memq 'backwards (debug-options))
+      n
+      (- (stack-length the-last-stack) n 1)))
+
 
 ;;; {Trace}
 ;;;