diff --git a/lib/awful.lua b/lib/awful.lua
index 9f9c35af9..b6b564608 100644
--- a/lib/awful.lua
+++ b/lib/awful.lua
@@ -15,6 +15,7 @@ else
 end
 
 -- Grab environment we need
+local string = string
 local assert = assert
 local loadstring = loadstring
 local ipairs = ipairs
@@ -702,8 +703,10 @@ function P.prompt(args, textbox, exe_callback, completion_callback)
             elseif key == "Right" then
                 cur_pos = cur_pos + 1
             else
-                command = command:sub(1, cur_pos - 1) .. key .. command:sub(cur_pos)
-                cur_pos = cur_pos + 1
+                if string.len(key) == 1 then
+                    command = command:sub(1, cur_pos - 1) .. key .. command:sub(cur_pos)
+                    cur_pos = cur_pos + 1
+                end
             end
             if cur_pos < 1 then
                 cur_pos = 1
diff --git a/lua.c b/lua.c
index 36de23aaa..a48f3a64e 100644
--- a/lua.c
+++ b/lua.c
@@ -453,6 +453,23 @@ luaA_openlib(lua_State *L, const char *name,
     luaL_register(L, name, methods);
 }
 
+static int
+luaA_mbstrlen(lua_State *L)
+{
+    const char *cmd = luaL_checkstring(L, 1);
+    lua_pushnumber(L, mbstowcs(NULL, NONULL(cmd), 0));
+    return 1;
+}
+
+static void
+luaA_fixups(lua_State *L)
+{
+    lua_getglobal(L, "string");
+    lua_pushcfunction(L, luaA_mbstrlen);
+    lua_setfield(L, -2, "len");
+    lua_pop(L, 1);
+}
+
 /** Initialize the Lua VM
  */
 void
@@ -497,6 +514,8 @@ luaA_init(void)
 
     luaL_openlibs(L);
 
+    luaA_fixups(L);
+
     /* Export awesome lib */
     luaL_register(L, "awesome", awesome_lib);