diff --git a/lib/command.rb b/lib/command.rb
index 30b69d9411c3a0802e0fbefedc595281ba3bbe10..4292d22bf62efc879a74e1f747523866cc7d8ac4 100644
--- a/lib/command.rb
+++ b/lib/command.rb
@@ -58,12 +58,13 @@ class Command
 		end
 
 		def reply(stanza=nil)
-			stanza ||= iq.reply.tap { |reply|
-				reply.status = :executing
-			}
+			stanza ||= iq.reply.tap { |reply| reply.status = :executing }
 			yield stanza if block_given?
 			COMMAND_MANAGER.write(stanza).then { |new_iq|
 				@iq = new_iq
+			}.catch_only(Blather::Stanza::Iq) { |new_iq|
+				@iq = new_iq if new_iq.set?
+				EMPromise.reject(new_iq)
 			}.catch_only(SessionManager::Timeout) do
 				EMPromise.reject(Timeout.new)
 			end
diff --git a/test/test_command.rb b/test/test_command.rb
new file mode 100644
index 0000000000000000000000000000000000000000..da8809c44583ccef46ddf780d33ccc9c92f19ae3
--- /dev/null
+++ b/test/test_command.rb
@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+require "test_helper"
+require "command"
+
+Command::COMMAND_MANAGER = Minitest::Mock.new
+
+class CommandTest < Minitest::Test
+	def test_cancel_finishes
+		blather = Minitest::Mock.new
+		iq1 = Blather::Stanza::Iq::Command.new
+		iq1.from = "test@example.com"
+		iq1.id = "test-id"
+		iq1.sessionid = "session-id"
+
+		# The library digests the sessionID I give it...
+		session = iq1.sessionid
+
+		iq2 = Blather::Stanza::Iq::Command.new
+		iq2.from = "test@example.com"
+		iq2.id = "cancel-id"
+		iq2.sessionid = "session-id"
+		iq2.action = :cancel
+
+		Command::COMMAND_MANAGER.expect(
+			:write,
+			EMPromise.reject(iq2),
+			[Matching.new do |iq|
+				assert_equal "test-id", iq.id
+				assert_equal session, iq.sessionid
+			end]
+		)
+
+		blather.expect(
+			:<<,
+			nil,
+			[Matching.new do |iq|
+				assert "canceled", iq.status
+				assert_equal "cancel-id", iq.id
+				assert_equal session, iq.sessionid
+			end]
+		)
+
+		execute_command(iq1, blather: blather) { |cmd|
+			cmd.reply.then do
+				raise "Should have cancelled"
+			end
+		}.then do
+			assert_mock blather
+			assert_mock Command::COMMAND_MANAGER
+		end
+	end
+	em :test_cancel_finishes
+end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 1e6bb86529df34269766adf8eee82af3a6e42975..f397d1555d0275e6d0e5671843551219f73db4ad 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -118,6 +118,19 @@ BLATHER = Class.new {
 	def <<(*); end
 }.new.freeze
 
+def execute_command(
+	iq=Blather::Stanza::Iq::Command.new.tap { |i| i.from = "test@example.com" },
+	blather: BLATHER,
+	&blk
+)
+	Command::Execution.new(
+		Minitest::Mock.new,
+		blather,
+		:to_s.to_proc,
+		iq
+	).execute(&blk).sync
+end
+
 class Matching
 	def initialize(&block)
 		@block = block
diff --git a/test/test_registration.rb b/test/test_registration.rb
index 00b75e51761fbad390c517783391c723f2df9f7f..08b18fc0f5f30f3517d6149c381ea9698b30bcd6 100644
--- a/test/test_registration.rb
+++ b/test/test_registration.rb
@@ -4,19 +4,6 @@ require "test_helper"
 require "customer"
 require "registration"
 
-def execute_command(
-	iq=Blather::Stanza::Iq::Command.new.tap { |i| i.from = "test@example.com" },
-	blather: BLATHER,
-	&blk
-)
-	Command::Execution.new(
-		Minitest::Mock.new,
-		blather,
-		:to_s.to_proc,
-		iq
-	).execute(&blk).sync
-end
-
 class RegistrationTest < Minitest::Test
 	def test_for_registered
 		sgx = OpenStruct.new(