diff --git a/pkgs/development/interpreters/python/pypy/default.nix b/pkgs/development/interpreters/python/pypy/default.nix
index 7779b3fbba8f..fa97386d68ce 100644
--- a/pkgs/development/interpreters/python/pypy/default.nix
+++ b/pkgs/development/interpreters/python/pypy/default.nix
@@ -120,14 +120,16 @@ stdenv.mkDerivation rec {
   dontPatchShebangs = true;
   disallowedReferences = [ python ];
 
-  # fix compiler error in curses cffi module, where char* != const char*
-  NIX_CFLAGS_COMPILE =
-    if stdenv.cc.isClang then "-Wno-error=incompatible-function-pointer-types" else null;
-  C_INCLUDE_PATH = lib.makeSearchPathOutput "dev" "include" buildInputs;
-  LIBRARY_PATH = lib.makeLibraryPath buildInputs;
-  LD_LIBRARY_PATH = lib.makeLibraryPath (
-    builtins.filter (x: x.outPath != stdenv.cc.libc.outPath or "") buildInputs
-  );
+  env = {
+    # fix compiler error in curses cffi module, where char* != const char*
+    NIX_CFLAGS_COMPILE =
+      if stdenv.cc.isClang then "-Wno-error=incompatible-function-pointer-types" else null;
+    C_INCLUDE_PATH = lib.makeSearchPathOutput "dev" "include" buildInputs;
+    LIBRARY_PATH = lib.makeLibraryPath buildInputs;
+    LD_LIBRARY_PATH = lib.makeLibraryPath (
+      builtins.filter (x: x.outPath != stdenv.cc.libc.outPath or "") buildInputs
+    );
+  };
 
   patches = [
     ./dont_fetch_vendored_deps.patch