diff --git a/graphgif.scm b/graphgif.scm
index 557121f..f60dd0b 100644
--- a/graphgif.scm
+++ b/graphgif.scm
@@ -179,6 +179,15 @@
 ;; ALGORITHMS!!! ;;
 ;;;;;;;;;;;;;;;;;;;
 
+(define (lex< a b)
+  (cond
+   [(and (number? a) (number? b)) (< a b)]
+   [(and (null? a) (null? b)) #f]
+   [(and (pair? a) (null? b)) #f]
+   [(and (null? a) (pair? b)) #t]
+   [(= (car a) (car b)) (lex< (cdr a) (cdr b))]
+   [else (< (car a) (car b))]))
+
 ;; Heap algorithms
 (define-public (heap-insert priority item heap)
   (define (fix-up! i heap)
@@ -187,7 +196,7 @@
 	(let* ([parent (quotient (1- i) 2)]
 	       [i-priority (car (vector-ref heap i))]
 	       [parent-priority (car (vector-ref heap parent))])
-	  (when (<= i-priority parent-priority)
+	  (when (lex< i-priority parent-priority)
 	    (vector-swap! heap i parent))
 	  (fix-up! parent heap))))
   (fix-up! (vector-length heap) (vector-append heap (vector (cons priority item)))))
@@ -202,8 +211,8 @@
 	   [right (1+ left)])
       (if (< left len)
 	  (let ([min (if (< right len)
-			 (argmin (compose car (partial vector-ref heap)) i left right)
-			 (argmin (compose car (partial vector-ref heap)) i left))])
+			 (argmin (compose car (partial vector-ref heap)) lex< i left right)
+			 (argmin (compose car (partial vector-ref heap)) lex< i left))])
 	    (if (= min i)
 		heap
 		(begin