diff --git a/elixir/apps/api/lib/api/client/channel.ex b/elixir/apps/api/lib/api/client/channel.ex
index bc171a9dd..fefd1e56b 100644
--- a/elixir/apps/api/lib/api/client/channel.ex
+++ b/elixir/apps/api/lib/api/client/channel.ex
@@ -900,6 +900,13 @@ defmodule API.Client.Channel do
     end
   end
 
+  # Catch-all for unknown messages
+  def handle_in(message, payload, socket) do
+    Logger.error("Unknown client message", message: message, payload: payload)
+
+    {:reply, {:error, %{reason: :unknown_message}}, socket}
+  end
+
   defp select_relays(socket, except_ids \\ []) do
     {:ok, relays} =
       Relays.all_connected_relays_for_account(socket.assigns.subject.account, except_ids)
diff --git a/elixir/apps/api/lib/api/gateway/channel.ex b/elixir/apps/api/lib/api/gateway/channel.ex
index 200c2eacd..7e8783ca2 100644
--- a/elixir/apps/api/lib/api/gateway/channel.ex
+++ b/elixir/apps/api/lib/api/gateway/channel.ex
@@ -657,6 +657,13 @@ defmodule API.Gateway.Channel do
     end
   end
 
+  # Catch-all for unknown messages
+  def handle_in(message, payload, socket) do
+    Logger.error("Unknown gateway message", message: message, payload: payload)
+
+    {:reply, {:error, %{reason: :unknown_message}}, socket}
+  end
+
   defp encode_ref(socket, tuple) do
     ref =
       tuple
diff --git a/elixir/apps/api/lib/api/relay/channel.ex b/elixir/apps/api/lib/api/relay/channel.ex
index 4c14f957e..7acb97ef4 100644
--- a/elixir/apps/api/lib/api/relay/channel.ex
+++ b/elixir/apps/api/lib/api/relay/channel.ex
@@ -2,6 +2,7 @@ defmodule API.Relay.Channel do
   use API, :channel
   alias Domain.Relays
   require OpenTelemetry.Tracer
+  require Logger
 
   @impl true
   def join("relay", %{"stamp_secret" => stamp_secret}, socket) do
@@ -45,4 +46,12 @@ defmodule API.Relay.Channel do
       {:noreply, socket}
     end
   end
+
+  # Catch-all for unknown messages
+  @impl true
+  def handle_in(message, payload, socket) do
+    Logger.error("Unknown relay message", message: message, payload: payload)
+
+    {:reply, {:error, %{reason: :unknown_message}}, socket}
+  end
 end
diff --git a/elixir/apps/api/test/api/client/channel_test.exs b/elixir/apps/api/test/api/client/channel_test.exs
index f6366aa2c..afa4d6411 100644
--- a/elixir/apps/api/test/api/client/channel_test.exs
+++ b/elixir/apps/api/test/api/client/channel_test.exs
@@ -2384,4 +2384,11 @@ defmodule API.Client.ChannelTest do
       assert client.id == client_id
     end
   end
+
+  describe "handle_in/3 for unknown messages" do
+    test "it doesn't crash", %{socket: socket} do
+      ref = push(socket, "unknown_message", %{})
+      assert_reply ref, :error, %{reason: :unknown_message}
+    end
+  end
 end
diff --git a/elixir/apps/api/test/api/gateway/channel_test.exs b/elixir/apps/api/test/api/gateway/channel_test.exs
index 713b01a1a..e3b0b1af3 100644
--- a/elixir/apps/api/test/api/gateway/channel_test.exs
+++ b/elixir/apps/api/test/api/gateway/channel_test.exs
@@ -1181,4 +1181,11 @@ defmodule API.Gateway.ChannelTest do
       assert upserted_activity.account_id == account.id
     end
   end
+
+  describe "handle_in/3 for unknown messages" do
+    test "it doesn't crash", %{socket: socket} do
+      ref = push(socket, "unknown_message", %{})
+      assert_reply ref, :error, %{reason: :unknown_message}
+    end
+  end
 end
diff --git a/elixir/apps/api/test/api/relay/channel_test.exs b/elixir/apps/api/test/api/relay/channel_test.exs
index 687f990f0..cd4dc5922 100644
--- a/elixir/apps/api/test/api/relay/channel_test.exs
+++ b/elixir/apps/api/test/api/relay/channel_test.exs
@@ -52,4 +52,11 @@ defmodule API.Relay.ChannelTest do
       assert_push "init", %{}
     end
   end
+
+  describe "handle_in/3 for unknown messages" do
+    test "it doesn't crash", %{socket: socket} do
+      ref = push(socket, "unknown_message", %{})
+      assert_reply ref, :error, %{reason: :unknown_message}
+    end
+  end
 end