diff -Naur old/stdlib/.depend new/stdlib/.depend
--- old/stdlib/.depend	2014-06-22 18:34:31.298480318 +0200
+++ new/stdlib/.depend	2014-06-22 18:34:17.522479966 +0200
@@ -147,10 +147,10 @@
     digest.cmx char.cmx array.cmx random.cmi
 scanf.cmo : string.cmi printf.cmi pervasives.cmi list.cmi \
     camlinternalFormatBasics.cmi camlinternalFormat.cmi bytes.cmi buffer.cmi \
-    scanf.cmi
+    weak.cmi scanf.cmi
 scanf.cmx : string.cmx printf.cmx pervasives.cmx list.cmx \
     camlinternalFormatBasics.cmx camlinternalFormat.cmx bytes.cmx buffer.cmx \
-    scanf.cmi
+    weak.cmx scanf.cmi
 set.cmo : list.cmi set.cmi
 set.cmx : list.cmx set.cmi
 sort.cmo : array.cmi sort.cmi
diff -Naur old/stdlib/Makefile.shared new/stdlib/Makefile.shared
--- old/stdlib/Makefile.shared	2014-06-22 18:33:54.426479374 +0200
+++ new/stdlib/Makefile.shared	2014-06-22 18:33:42.866479078 +0200
@@ -30,9 +30,9 @@
   camlinternalLazy.cmo lazy.cmo stream.cmo \
   buffer.cmo camlinternalFormat.cmo printf.cmo \
   arg.cmo printexc.cmo gc.cmo \
-  digest.cmo random.cmo hashtbl.cmo format.cmo scanf.cmo callback.cmo \
+  digest.cmo random.cmo hashtbl.cmo format.cmo weak.cmo scanf.cmo callback.cmo \
   camlinternalOO.cmo oo.cmo camlinternalMod.cmo \
-  genlex.cmo weak.cmo \
+  genlex.cmo \
   filename.cmo complex.cmo \
   arrayLabels.cmo listLabels.cmo bytesLabels.cmo \
   stringLabels.cmo moreLabels.cmo stdLabels.cmo
diff -Naur old/stdlib/scanf.ml new/stdlib/scanf.ml
--- old/stdlib/scanf.ml	2014-06-22 18:31:52.162476244 +0200
+++ new/stdlib/scanf.ml	2014-06-22 18:31:35.010475805 +0200
@@ -390,12 +390,31 @@
   let from_file_bin = open_in_bin;;
 
   let memo_from_ic =
-    let memo = ref [] in
+    let module IcMemo = Weak.Make (struct
+      type t = Pervasives.in_channel
+      let equal ic1 ic2 = ic1 = ic2
+      let hash ic = Hashtbl.hash ic
+    end) in
+    let module PairMemo = Weak.Make (struct
+      type t = Pervasives.in_channel * in_channel
+      let equal (ic1, _) (ic2, _) = ic1 = ic2
+      let hash (ic, _) = Hashtbl.hash ic
+    end) in
+    let ic_memo = IcMemo.create 16 in
+    let pair_memo = PairMemo.create 16 in
+    let rec finaliser ((ic, _) as pair) =
+      if IcMemo.mem ic_memo ic then (
+        Gc.finalise finaliser pair;
+        PairMemo.add pair_memo pair;
+      ) in
     (fun scan_close_ic ic ->
-     try List.assq ic !memo with
+     try snd (PairMemo.find pair_memo (ic, stdin)) with
      | Not_found ->
        let ib = from_ic scan_close_ic (From_channel ic) ic in
-       memo := (ic, ib) :: !memo;
+       let pair = (ic, ib) in
+       IcMemo.add ic_memo ic;
+       Gc.finalise finaliser pair;
+       PairMemo.add pair_memo pair;
        ib)
   ;;