diff --git a/rebar.config b/rebar.config
index 81f3dc84c..1316ffe17 100644
--- a/rebar.config
+++ b/rebar.config
@@ -56,7 +56,7 @@
           {rebar_elixir_plugin, ".*", {git, "https://github.com/processone/rebar_elixir_plugin", "0.1.0"}}}},
         {if_var_true, sqlite,
          {sqlite3, ".*", {git, "https://github.com/processone/erlang-sqlite3", {tag, "1.1.12"}}}},
-        {stringprep, ".*", {git, "https://github.com/processone/stringprep", {tag, "1.0.25"}}},
+        {stringprep, ".*", {git, "https://github.com/processone/stringprep", "6d143ebcacaafe3a8adc669300a8ad001402b3d8"}},
         {if_var_true, stun,
          {stun, ".*", {git, "https://github.com/processone/stun", {tag, "1.0.43"}}}},
         {xmpp, ".*", {git, "https://github.com/processone/xmpp", {tag, "1.5.3"}}},
diff --git a/src/mod_vcard.erl b/src/mod_vcard.erl
index 85734b358..e7cfff819 100644
--- a/src/mod_vcard.erl
+++ b/src/mod_vcard.erl
@@ -424,9 +424,9 @@ set_vcard(User, LServer, VCARD) ->
 
 -spec string2lower(binary()) -> binary().
 string2lower(String) ->
-    case stringprep:tolower(String) of
+    case stringprep:tolower_nofilter(String) of
       Lower when is_binary(Lower) -> Lower;
-      error -> str:to_lower(String)
+      error -> String
     end.
 
 -spec mk_tfield(binary(), binary(), binary()) -> xdata_field().