diff --git a/src/core/Heap.ml b/src/core/Heap.ml
index 12fa608c..ed9884bb 100644
--- a/src/core/Heap.ml
+++ b/src/core/Heap.ml
@@ -124,17 +124,22 @@ module Make(Elt : RANKED) = struct
   *)
 
   let remove_min ({heap} as s) =
-    if Vec.size heap=0 then raise Not_found;
-    let x = Vec.get heap 0 in
-    let new_hd = Vec.pop heap in (* new head *)
-    Vec.set heap 0 new_hd;
-    Elt.set_idx new_hd 0;
-    (* remove [x]. do it after [new_hd.idx<-0] in case [x==new_hd] *)
-    Elt.set_idx x _absent_index;
-    (* enforce heap property again *)
-    if Vec.size heap > 1 then (
-      percolate_down s new_hd;
-    );
-    x
+    match Vec.size heap with
+    | 0 -> raise Not_found
+    | 1 ->
+      let x = Vec.pop heap in
+      Elt.set_idx x _absent_index;
+      x
+    | _ ->
+      let x = Vec.get heap 0 in
+      let new_hd = Vec.pop heap in (* heap.last() *)
+      Vec.set heap 0 new_hd;
+      Elt.set_idx x _absent_index;
+      Elt.set_idx new_hd 0;
+      (* enforce heap property again *)
+      if Vec.size heap > 1 then (
+        percolate_down s new_hd;
+      );
+      x
 
 end [@@inline]