diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8d246d4..dc19c64 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,14 @@ Full module documentation: [hexdocs.pm/mob_dev](https://hexdocs.pm/mob_dev).
 
 ## [Unreleased]
 
+### Fixed
+
+- **`mix mob.deploy` silently ignored unknown options.** `-d` was never aliased
+  to `--device` here — `mob.connect` has aliased it all along — so
+  `mix mob.deploy -d <udid>` deployed to *every* connected device instead of
+  the one named, without a word. A typo'd `--devcie` did the same. Parsing is
+  strict now and the run refuses, naming the offending options.
+
 ### Changed
 
 - **`mix mob.deploy` no longer exits 0 after shipping nothing.** Four ways it
diff --git a/lib/mix/tasks/mob.deploy.ex b/lib/mix/tasks/mob.deploy.ex
index 31526ef..1b79bc2 100644
--- a/lib/mix/tasks/mob.deploy.ex
+++ b/lib/mix/tasks/mob.deploy.ex
@@ -179,7 +179,18 @@ defmodule Mix.Tasks.Mob.Deploy do
 
   @impl Mix.Task
   def run(args) do
-    {opts, _, _} = OptionParser.parse(args, switches: @switches)
+    {opts, _argv, invalid} =
+      OptionParser.parse(args, strict: @switches, aliases: [d: :device])
+
+    # `switches:` silently discards anything it does not recognise, so
+    # `mix mob.deploy -d <udid>` — `-d` was never aliased here, though
+    # `mob.connect` has aliased it all along — deployed to every device
+    # instead of the one named, and said nothing. A typo'd `--devcie` did the
+    # same. `strict:` collects them so the run can refuse rather than do
+    # something other than what was asked.
+    unless invalid == [] do
+      Mix.raise(invalid_options_message(invalid))
+    end
 
     # Under --json, stdout must carry ONE document and nothing else. Every
     # progress line in this task, the deployer and the native build is a plain
@@ -410,6 +421,21 @@ defmodule Mix.Tasks.Mob.Deploy do
     end
   end
 
+  @doc """
+  The error for options the task does not accept.
+
+  Names them, because the failure this replaces was silent: the flag was
+  dropped and the deploy proceeded as if it had never been passed.
+  """
+  @spec invalid_options_message([{String.t(), String.t() | nil}]) :: String.t()
+  def invalid_options_message(invalid) do
+    names = invalid |> Enum.map(&elem(&1, 0)) |> Enum.join(", ")
+
+    "Unknown option(s): #{names}\n\n" <>
+      "Run `mix help mob.deploy` for the accepted options. " <>
+      "Short forms are not aliases except `-d` for `--device`."
+  end
+
   @doc """
   The machine-readable result of a finished deploy.
 
diff --git a/test/mix/tasks/mob_deploy_beam_flags_test.exs b/test/mix/tasks/mob_deploy_beam_flags_test.exs
index f619a2c..be032e5 100644
--- a/test/mix/tasks/mob_deploy_beam_flags_test.exs
+++ b/test/mix/tasks/mob_deploy_beam_flags_test.exs
@@ -463,4 +463,19 @@ defmodule Mix.Tasks.Mob.DeployBeamFlagsTest do
       assert result |> Jason.encode!() |> Jason.decode!() == result
     end
   end
+
+  describe "unknown options are refused, not discarded" do
+    # `mix mob.deploy -d <udid>` deployed to every device instead of the one
+    # named, and said nothing: `-d` was never aliased here even though
+    # `mob.connect` has aliased it all along, and `switches:` silently drops
+    # what it does not recognise. Found while verifying MOB-151, when two
+    # native builds went to the wrong device for this reason.
+    test "the message names the offending options" do
+      message = Deploy.invalid_options_message([{"-d", nil}, {"--devcie", "x"}])
+
+      assert message =~ "-d"
+      assert message =~ "--devcie"
+      assert message =~ "Unknown option"
+    end
+  end
 end
diff --git a/test/mob_dev/wiring_test.exs b/test/mob_dev/wiring_test.exs
index d2690e7..7aab467 100644
--- a/test/mob_dev/wiring_test.exs
+++ b/test/mob_dev/wiring_test.exs
@@ -179,4 +179,33 @@ defmodule MobDev.WiringTest do
                ~r/emit_json\(opts, \[\], \[\], \[\], "Native build failed"\)\s*Mix\.raise/
     end
   end
+
+  describe "mob.deploy refuses what it does not recognise" do
+    # `-d` was never aliased here, and `switches:` drops unknown flags in
+    # silence — so `mix mob.deploy -d <udid>` deployed to every device instead
+    # of the one named. Source assertions because the parse happens inside
+    # run/1, before anything testable is reached.
+    test "-d is aliased to --device, matching mob.connect" do
+      source = @deploy_task
+
+      assert source =~ "aliases: [d: :device]"
+    end
+
+    test "parsing is strict, so nothing is dropped in silence" do
+      # `switches:` puts an unrecognised flag in `invalid` and carries on;
+      # `strict:` is what makes the run able to refuse. Reverting this one word
+      # restores the silent-ignore.
+      source = @deploy_task
+
+      assert source =~ "OptionParser.parse(args, strict: @switches, aliases: [d: :device])"
+      refute source =~ "OptionParser.parse(args, switches: @switches)"
+    end
+
+    test "the run raises rather than proceeding" do
+      source = @deploy_task
+
+      assert source =~
+               ~r/unless invalid == \[\] do\s*Mix\.raise\(invalid_options_message\(invalid\)\)/
+    end
+  end
 end