diff --git a/pkgs/development/libraries/libmcrypt/default.nix b/pkgs/development/libraries/libmcrypt/default.nix
index d1f048ee2c53..42164052075e 100644
--- a/pkgs/development/libraries/libmcrypt/default.nix
+++ b/pkgs/development/libraries/libmcrypt/default.nix
@@ -11,8 +11,12 @@ stdenv.mkDerivation rec {
 
   buildInputs = lib.optional stdenv.isDarwin darwin.cctools;
 
-  configureFlags = lib.optionals disablePosixThreads
-    [ "--disable-posix-threads" ];
+  configureFlags = lib.optionals disablePosixThreads [ "--disable-posix-threads" ]
+    ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
+      # AC_FUNC_MALLOC is broken on cross builds.
+      "ac_cv_func_malloc_0_nonnull=yes"
+      "ac_cv_func_realloc_0_nonnull=yes"
+    ];
 
   meta = {
     description = "Replacement for the old crypt() package and crypt(1) command, with extensions";