diff --git a/VERSION b/VERSION
index 0516ac10..0041a435 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.1.65
+1.1.66
diff --git a/lib/supavisor/client_handler.ex b/lib/supavisor/client_handler.ex
index 4c46f5fe..495f98c0 100644
--- a/lib/supavisor/client_handler.ex
+++ b/lib/supavisor/client_handler.ex
@@ -154,15 +154,11 @@ defmodule Supavisor.ClientHandler do
         Logger.debug("ClientHandler: Client startup message: #{inspect(hello)}")
         {type, {user, tenant_or_alias, db_name}} = HH.parse_user_info(hello.payload)
 
-        not_allowed = ["\"", "\\"]
+        # Validate user and db_name according to PostgreSQL rules.
+        # The rules are: 1-63 characters, alphanumeric, underscore and $
+        rule = ~r/^[a-z_][a-z0-9_$]*$/
 
-        if String.contains?(user, not_allowed) or String.contains?(db_name, not_allowed) do
-          reason = "Invalid characters in user or db_name"
-          Logger.error("ClientHandler: #{inspect(reason)}")
-          Telem.client_join(:fail, data.id)
-          HH.send_error(data.sock, "XX000", "Authentication error, reason: #{inspect(reason)}")
-          {:stop, {:shutdown, :invalid_characters}}
-        else
+        if user =~ rule and db_name =~ rule do
           log_level =
             case hello.payload["options"]["log_level"] do
               nil -> nil
@@ -173,6 +169,12 @@ defmodule Supavisor.ClientHandler do
 
           {:keep_state, %{data | log_level: log_level},
            {:next_event, :internal, {:hello, {type, {user, tenant_or_alias, db_name}}}}}
+        else
+          reason = "Invalid format for user or db_name"
+          Logger.error("ClientHandler: #{inspect(reason)}")
+          Telem.client_join(:fail, tenant_or_alias)
+          HH.send_error(data.sock, "XX000", "Authentication error, reason: #{inspect(reason)}")
+          {:stop, {:shutdown, :invalid_format}}
         end
 
       {:error, error} ->
diff --git a/test/integration/proxy_test.exs b/test/integration/proxy_test.exs
index 689912f8..168146ba 100644
--- a/test/integration/proxy_test.exs
+++ b/test/integration/proxy_test.exs
@@ -249,12 +249,12 @@ defmodule Supavisor.Integration.ProxyTest do
     assert [%Postgrex.Result{rows: [["1"]]}] = P.SimpleConnection.call(pid, {:query, "select 1;"})
   end
 
-  test "invalid characters in user or db_name" do
+  test "invalid format for user or db_name" do
     Process.flag(:trap_exit, true)
     db_conf = Application.get_env(:supavisor, Repo)
 
     url =
-      "postgresql://user\"user.#{@tenant}:#{db_conf[:password]}@#{db_conf[:hostname]}:#{Application.get_env(:supavisor, :proxy_port_transaction)}/postgres\\\\\\\\\"\\"
+      "postgresql://user\"user.#{@tenant}:#{db_conf[:password]}@#{db_conf[:hostname]}:#{Application.get_env(:supavisor, :proxy_port_transaction)}/post gres\\\\\\\\\"\\"
 
     assert {:error,
             {_,
@@ -262,8 +262,7 @@ defmodule Supavisor.Integration.ProxyTest do
               %Postgrex.Error{
                 postgres: %{
                   code: :internal_error,
-                  message:
-                    "Authentication error, reason: \"Invalid characters in user or db_name\"",
+                  message: "Authentication error, reason: \"Invalid format for user or db_name\"",
                   pg_code: "XX000",
                   severity: "FATAL",
                   unknown: "FATAL"