diff --git a/pkgs/development/ocaml-modules/zarith/default.nix b/pkgs/development/ocaml-modules/zarith/default.nix
index c97078c62ed..f0cb5a59485 100644
--- a/pkgs/development/ocaml-modules/zarith/default.nix
+++ b/pkgs/development/ocaml-modules/zarith/default.nix
@@ -6,9 +6,9 @@
 let source =
   if stdenv.lib.versionAtLeast ocaml.version "4.02"
   then {
-    version = "1.9.1";
-    url = https://github.com/ocaml/Zarith/archive/release-1.9.1.tar.gz;
-    sha256 = "0pfa271476dic5pvn6kxz3dfswxs6kqm2cxmhdx5xq2ayca05gj9";
+    version = "1.9";
+    url = https://github.com/ocaml/Zarith/archive/release-1.9.tar.gz;
+    sha256 = "1xrqcaj5gp52xp4ybpnblw8ciwlgrr0zi7rg7hnk8x83isjkpmwx";
   } else {
     version = "1.3";
     url = http://forge.ocamlcore.org/frs/download.php/1471/zarith-1.3.tgz;
@@ -26,9 +26,8 @@ stdenv.mkDerivation rec {
   propagatedBuildInputs = [ gmp ];
 
   patchPhase = "patchShebangs ./z_pp.pl";
-  configurePhase = ''
-    ./configure -installdir $out/lib/ocaml/${ocaml.version}/site-lib
-  '';
+  dontAddPrefix = true;
+  configureFlags = [ "-installdir ${placeholder "out"}/lib/ocaml/${ocaml.version}/site-lib" ];
 
   preInstall = "mkdir -p $out/lib/ocaml/${ocaml.version}/site-lib/stublibs";