diff --git a/pkgs/development/interpreters/python/cpython/3.6/default.nix b/pkgs/development/interpreters/python/cpython/3.6/default.nix
index ebf621d5057..2acca2b8a3c 100644
--- a/pkgs/development/interpreters/python/cpython/3.6/default.nix
+++ b/pkgs/development/interpreters/python/cpython/3.6/default.nix
@@ -34,7 +34,7 @@ let
   sitePackages = "lib/${libPrefix}/site-packages";
 
   buildInputs = filter (p: p != null) [
-    zlib bzip2 lzma gdbm sqlite readline ncurses openssl ]
+    zlib bzip2 expat lzma libffi gdbm sqlite readline ncurses openssl ]
     ++ optionals x11Support [ tcl tk libX11 xproto ]
     ++ optionals stdenv.isDarwin [ CF configd ];