diff --git a/default.nix b/default.nix
index 49073fa4..a0027949 100644
--- a/default.nix
+++ b/default.nix
@@ -106,7 +106,7 @@ let
 
     # Programs for generating Nix expressions from Cabal and Stack
     # files.
-    nix-tools = self.callPackage ./nix-tools {};
+    nix-tools = self.callPackage ./nix-tools { inherit fetchExternal; };
 
     # Snapshots of Hackage and Stackage, converted to Nix expressions,
     # regularly updated.
diff --git a/nix-tools/default.nix b/nix-tools/default.nix
index b4a2e93d..ee84f9c3 100644
--- a/nix-tools/default.nix
+++ b/nix-tools/default.nix
@@ -1,6 +1,12 @@
-{ symlinkJoin, mkCabalProjectPkgSet }:
+{ symlinkJoin, fetchExternal, mkCabalProjectPkgSet }:
 
 let
+  src = fetchExternal {
+    name     = "nix-tools-src";
+    specJSON = ./nix-tools-src.json;
+    override = "nix-tools";
+  };
+
   pkgSet = mkCabalProjectPkgSet {
     plan-pkgs = import ./pkgs.nix;
     pkg-def-extras = [];
@@ -10,6 +16,10 @@ let
         packages.time-compat.components.library.doExactConfig = true;
         packages.time-locale-compat.components.library.doExactConfig = true;
       }
+
+      {
+        packages.nix-tools.src = src;
+      }
     ];
   };
 
diff --git a/nix-tools/nix-tools-src.json b/nix-tools/nix-tools-src.json
new file mode 100644
index 00000000..2d93547f
--- /dev/null
+++ b/nix-tools/nix-tools-src.json
@@ -0,0 +1,7 @@
+{
+  "url": "https://github.com/input-output-hk/nix-tools",
+  "rev": "38bf6fd0adef4d22fe06def521f5d793c081f6ed",
+  "date": "2019-03-20T12:40:31+10:00",
+  "sha256": "0y8xap5cvc9rssjjvlgv6lyi8ixpxnq675r3gkz2ix7hrsgk8989",
+  "fetchSubmodules": false
+}