diff --git a/qtest/Makefile b/qtest/Makefile
index 39705a4..48a2984 100644
--- a/qtest/Makefile
+++ b/qtest/Makefile
@@ -1,6 +1,6 @@
 
 QTEST_PREAMBLE=''
-DONTTEST=../src/iterLabels.ml ../src/mkflags.ml
+DONTTEST=../src/iterLabels.ml ../src/mkflags.ml ../src/mkshims.ml ../src/bigarray/mkshims.ml
 QTESTABLE=$(filter-out $(DONTTEST), \
 	$(wildcard ../src/*.ml) \
 	$(wildcard ../src/*.mli) \
diff --git a/src/Iter.ml b/src/Iter.ml
index 40fd47d..71789df 100644
--- a/src/Iter.ml
+++ b/src/Iter.ml
@@ -3,6 +3,8 @@
 
 (** {1 Simple and Efficient Iterators} *)
 
+open Iter_shims_
+
 (** Iter abstract iterator type *)
 type 'a t = ('a -> unit) -> unit
 
diff --git a/src/bigarray/IterBigarray.ml b/src/bigarray/IterBigarray.ml
index 716f12c..903d437 100644
--- a/src/bigarray/IterBigarray.ml
+++ b/src/bigarray/IterBigarray.ml
@@ -3,7 +3,7 @@
 
 (** {1 Interface and Helpers for bigarrays} *)
 
-open! Bigarray
+open! IterBigarrayShims_
 
 let of_bigarray b yield =
   let len = Bigarray.Array1.dim b in
@@ -16,7 +16,7 @@ let mmap filename =
     let fd = Unix.openfile filename [Unix.O_RDONLY] 0 in
     let len = Unix.lseek fd 0 Unix.SEEK_END in
     let _ = Unix.lseek fd 0 Unix.SEEK_SET in
-    let b = Bigarray.Array1.map_file fd Bigarray.char Bigarray.c_layout false len in
+    let b = bigarray_map_file fd Bigarray.char Bigarray.c_layout false len in
     try
       of_bigarray b yield;
       Unix.close fd
diff --git a/src/bigarray/dune b/src/bigarray/dune
index 0c5d849..67aea21 100644
--- a/src/bigarray/dune
+++ b/src/bigarray/dune
@@ -3,8 +3,18 @@
   (name iter_bigarray)
   (public_name iter.bigarray)
   (libraries iter bigarray)
+  (modules IterBigarray IterBigarrayShims_)
   (wrapped false)
   (optional)
   (flags :standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string)
-  (ocamlopt_flags :standard (:include ../flambda.flags))
-  )
+  (ocamlopt_flags :standard (:include ../flambda.flags)))
+
+(executable
+  (name mkshims)
+  (modules mkshims)
+  (libraries dune.configurator))
+
+(rule
+  (targets IterBigarrayShims_.ml)
+  (deps mkshims.exe)
+  (action (with-stdout-to %{targets} (run ./mkshims.exe))))
diff --git a/src/bigarray/mkshims.ml b/src/bigarray/mkshims.ml
new file mode 100644
index 0000000..d24e42d
--- /dev/null
+++ b/src/bigarray/mkshims.ml
@@ -0,0 +1,17 @@
+
+module C = Configurator.V1
+
+let shims_pre_408 = "
+open! Bigarray
+let bigarray_map_file = Bigarray.Array1.map_file
+"
+let shims_post_408 = "
+let bigarray_map_file fd ty lay b len =
+  Unix.map_file fd ty lay b [| len |] |> Bigarray.array1_of_genarray
+"
+
+let () =
+  C.main ~name:"mkshims" (fun c ->
+    let version = C.ocaml_config_var_exn c "version" in
+    let major, minor = Scanf.sscanf version "%u.%u" (fun maj min -> maj, min) in
+    print_endline (if (major, minor) >= (4,8) then shims_post_408 else shims_post_408))
diff --git a/src/dune b/src/dune
index 7fc8a02..b8396d2 100644
--- a/src/dune
+++ b/src/dune
@@ -2,17 +2,24 @@
   (targets flambda.flags)
   (deps mkflags.ml)
   (mode fallback)
-  (action
-    (run ocaml ./mkflags.ml))
-  )
+  (action (run ocaml ./mkflags.ml)))
+
+(executable
+  (name mkshims)
+  (modules mkshims)
+  (libraries dune.configurator))
+
+(rule
+  (targets Iter_shims_.ml)
+  (deps mkshims.exe)
+  (action (with-stdout-to %{targets} (run ./mkshims.exe))))
 
 (library
   (name iter)
   (public_name iter)
   (wrapped false)
-  (modules Iter IterLabels)
+  (modules Iter IterLabels Iter_shims_)
   (flags :standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string -nolabels)
   (ocamlopt_flags :standard (:include flambda.flags))
-  (libraries bytes result)
-  )
+  (libraries bytes result))
 
diff --git a/src/mkshims.ml b/src/mkshims.ml
new file mode 100644
index 0000000..fb99ffe
--- /dev/null
+++ b/src/mkshims.ml
@@ -0,0 +1,11 @@
+
+module C = Configurator.V1
+
+let shims_pre_408 = "module Pervasives = Pervasives"
+let shims_post_408 = "module Pervasives = Stdlib"
+
+let () =
+  C.main ~name:"mkshims" (fun c ->
+    let version = C.ocaml_config_var_exn c "version" in
+    let major, minor = Scanf.sscanf version "%u.%u" (fun maj min -> maj, min) in
+    print_endline (if (major, minor) >= (4,8) then shims_post_408 else shims_post_408))