diff --git a/src/rebar_port_compiler.erl b/src/rebar_port_compiler.erl
index 2f419c9..3cc8fc1 100644
--- a/src/rebar_port_compiler.erl
+++ b/src/rebar_port_compiler.erl
@@ -254,7 +254,7 @@ default_env() ->
                                      " "])},
      {"DRIVER_LDFLAGS", lists:concat([" -L", code:lib_dir(erl_interface, lib),
                                       " -lerl_interface -lei"])},
-     {"ERLANG_ARCH", 8 * erlang:system_info(wordsize)},
+     {"ERLANG_ARCH", integer_to_list(8 * erlang:system_info(wordsize))},
      {"ERLANG_TARGET", erlang:system_info(system_architecture)}].