diff --git a/server.rb b/server.rb
index aece287..506d418 100644
--- a/server.rb
+++ b/server.rb
@@ -32,6 +32,10 @@ def diceroll(system, command)
     result, secret = bcdice.dice_command
     dices = bcdice.getRandResults.map {|dice| {faces: dice[1], value: dice[0]}}
 
+    if result.nil?
+      raise CommandError
+    end
+
     return result, secret, dices
   end
 end
@@ -59,9 +63,6 @@ def diceroll(system, command)
 
 get "/v1/diceroll" do
   result, secret, dices = diceroll(params[:system], params[:command])
-  if result.nil?
-    raise CommandError
-  end
 
   jsonp ok: true, result: result, secret: secret, dices: dices
 end
@@ -71,12 +72,11 @@ def diceroll(system, command)
     return BCDice::SYSTEMS.join("\n")
   end
 
-  result, secret, dices = diceroll(params[:sys] || "DiceBot", params[:text])
-
-  if result.nil?
-    "error"
-  else
+  begin
+    result, secret, dices = diceroll(params[:sys] || "DiceBot", params[:text])
     "onset" + result
+  rescue UnsupportedDicebot, CommandError
+    "error"
   end
 end
 
diff --git a/test/test_api.rb b/test/test_api.rb
index 10b371a..a45d510 100644
--- a/test/test_api.rb
+++ b/test/test_api.rb
@@ -111,6 +111,36 @@ def test_no_command
     assert_equal json["reason"], "unsupported command"
   end
 
+  def test_onset_list
+    get "/v1/onset?list=1"
+
+    list = last_response.body.split("\n")
+
+    assert last_response.ok?
+    assert_include list, "Amadeus"
+  end
+
+  def test_onset_diceroll
+    get "/v1/onset?sys=Cthulhu&text=1d20"
+
+    assert last_response.ok?
+    assert last_response.body.start_with?("onset: (1D20)")
+  end
+
+  def test_onset_unexpected_dicebot
+    get "/v1/onset?sys=AwesomeDicebot&text=1d20"
+
+    assert last_response.ok?
+    assert_equal last_response.body, "error"
+  end
+
+  def test_onset_unexpected_command
+    get "/v1/onset?sys=DiceBot&text=a"
+
+    assert last_response.ok?
+    assert_equal last_response.body, "error"
+  end
+
   def test_not_found
     get "/hogehoge"
     json = JSON.parse(last_response.body)