diff --git a/pkgs/applications/networking/irc/weechat/default.nix b/pkgs/applications/networking/irc/weechat/default.nix
index 060be8ab1eb..b9bc21c88e0 100644
--- a/pkgs/applications/networking/irc/weechat/default.nix
+++ b/pkgs/applications/networking/irc/weechat/default.nix
@@ -1,6 +1,6 @@
 { stdenv, fetchurl, ncurses, openssl, perl, python, aspell, gnutls
 , zlib, curl , pkgconfig, libgcrypt, ruby, lua5, tcl, guile
-, pythonPackages, cmake, makeWrapper, libobjc
+, pythonPackages, cmake, makeWrapper, libobjc, libiconv
 , extraBuildInputs ? [] }:
 
 stdenv.mkDerivation rec {
@@ -12,6 +12,9 @@ stdenv.mkDerivation rec {
     sha256 = "0kb8mykhzm7zcxsl6l6cia2n4nc9akiysg0v6d8xb51p3x002ibw";
   };
 
+  cmakeFlags = stdenv.lib.optional stdenv.isDarwin
+    "-DICONV_LIBRARY=${libiconv}/lib/libiconv.dylib";
+
   buildInputs = 
     [ ncurses perl python openssl aspell gnutls zlib curl pkgconfig
       libgcrypt ruby lua5 tcl guile pythonPackages.pycrypto makeWrapper