diff --git a/source/extensions/filters/http/ext_proc/ext_proc.cc b/source/extensions/filters/http/ext_proc/ext_proc.cc
index dfedb67f82dec..bb2673f664e39 100644
--- a/source/extensions/filters/http/ext_proc/ext_proc.cc
+++ b/source/extensions/filters/http/ext_proc/ext_proc.cc
@@ -50,6 +50,7 @@ Filter::StreamOpenState Filter::openStream() {
 }
 
 void Filter::onDestroy() {
+  ENVOY_LOG(trace, "onDestroy");
   // Make doubly-sure we no longer use the stream, as
   // per the filter contract.
   processing_complete_ = true;
@@ -461,6 +462,7 @@ void Filter::onReceiveMessage(std::unique_ptr<ProcessingResponse>&& r) {
     // We won't be sending anything more to the stream after we
     // receive this message.
     processing_complete_ = true;
+    cleanUpTimers();
     sendImmediateResponse(response->immediate_response());
     message_handled = true;
     break;
diff --git a/test/extensions/filters/http/ext_proc/filter_test.cc b/test/extensions/filters/http/ext_proc/filter_test.cc
index 22be455ee6c01..df872b98a3580 100644
--- a/test/extensions/filters/http/ext_proc/filter_test.cc
+++ b/test/extensions/filters/http/ext_proc/filter_test.cc
@@ -38,6 +38,7 @@ using Http::FilterHeadersStatus;
 using Http::FilterTrailersStatus;
 using Http::LowerCaseString;
 
+using testing::AnyNumber;
 using testing::Eq;
 using testing::Invoke;
 using testing::ReturnRef;
@@ -57,6 +58,19 @@ class HttpFilterTest : public testing::Test {
     EXPECT_CALL(*client_, start(_)).WillOnce(Invoke(this, &HttpFilterTest::doStart));
     EXPECT_CALL(encoder_callbacks_, dispatcher()).WillRepeatedly(ReturnRef(dispatcher_));
     EXPECT_CALL(decoder_callbacks_, dispatcher()).WillRepeatedly(ReturnRef(dispatcher_));
+    EXPECT_CALL(dispatcher_, createTimer_(_))
+        .Times(AnyNumber())
+        .WillRepeatedly(Invoke([this](Unused) {
+          // Create a mock timer that we can check at destruction time to see if
+          // all timers were disabled no matter what. MockTimer has default
+          // actions that we just have to enable properly here.
+          auto* timer = new Event::MockTimer();
+          EXPECT_CALL(*timer, enableTimer(_, _)).Times(AnyNumber());
+          EXPECT_CALL(*timer, disableTimer()).Times(AnyNumber());
+          EXPECT_CALL(*timer, enabled()).Times(AnyNumber());
+          timers_.push_back(timer);
+          return timer;
+        }));
 
     envoy::extensions::filters::http::ext_proc::v3alpha::ExternalProcessor proto_config{};
     if (!yaml.empty()) {
@@ -72,6 +86,15 @@ class HttpFilterTest : public testing::Test {
     request_headers_.setMethod("POST");
   }
 
+  void TearDown() override {
+    for (auto* t : timers_) {
+      // This will fail if, at the end of the test, we left any timers enabled.
+      // (This particular test suite does not actually let timers expire,
+      // although other test suites do.)
+      EXPECT_FALSE(t->enabled_);
+    }
+  }
+
   ExternalProcessorStreamPtr doStart(ExternalProcessorCallbacks& callbacks) {
     stream_callbacks_ = &callbacks;
 
@@ -214,13 +237,14 @@ class HttpFilterTest : public testing::Test {
   NiceMock<Stats::MockIsolatedStatsStore> stats_store_;
   FilterConfigSharedPtr config_;
   std::unique_ptr<Filter> filter_;
-  NiceMock<Event::MockDispatcher> dispatcher_;
+  testing::NiceMock<Event::MockDispatcher> dispatcher_;
   Http::MockStreamDecoderFilterCallbacks decoder_callbacks_;
   Http::MockStreamEncoderFilterCallbacks encoder_callbacks_;
   Http::TestRequestHeaderMapImpl request_headers_;
   Http::TestResponseHeaderMapImpl response_headers_;
   Http::TestRequestTrailerMapImpl request_trailers_;
   Http::TestResponseTrailerMapImpl response_trailers_;
+  std::vector<Event::MockTimer*> timers_;
 };
 
 // Using the default configuration, test the filter with a processor that
diff --git a/test/extensions/filters/http/ext_proc/ordering_test.cc b/test/extensions/filters/http/ext_proc/ordering_test.cc
index 65f98bd364207..af3cf936c1111 100644
--- a/test/extensions/filters/http/ext_proc/ordering_test.cc
+++ b/test/extensions/filters/http/ext_proc/ordering_test.cc
@@ -32,6 +32,7 @@ using Http::FilterHeadersStatus;
 using Http::FilterTrailersStatus;
 using Http::LowerCaseString;
 
+using testing::AnyNumber;
 using testing::Invoke;
 using testing::Return;
 using testing::ReturnRef;
@@ -535,9 +536,14 @@ TEST_F(OrderingTest, AddRequestTrailers) {
 TEST_F(OrderingTest, ImmediateResponseOnRequest) {
   initialize(absl::nullopt);
 
+  // MockTimer constructor sets up expectations in the Dispatcher class to wire it up
+  MockTimer* request_timer = new MockTimer(&dispatcher_);
+  EXPECT_CALL(*request_timer, enableTimer(kMessageTimeout, nullptr));
+  EXPECT_CALL(*request_timer, enabled()).Times(AnyNumber());
   EXPECT_CALL(stream_delegate_, send(_, false));
   sendRequestHeadersGet(true);
   EXPECT_CALL(encoder_callbacks_, sendLocalReply(Http::Code::InternalServerError, _, _, _, _));
+  EXPECT_CALL(*request_timer, disableTimer());
   sendImmediateResponse500();
   // The rest of the filter isn't necessarily called after this.
 }
@@ -546,14 +552,22 @@ TEST_F(OrderingTest, ImmediateResponseOnRequest) {
 TEST_F(OrderingTest, ImmediateResponseOnResponse) {
   initialize(absl::nullopt);
 
+  MockTimer* request_timer = new MockTimer(&dispatcher_);
+  EXPECT_CALL(*request_timer, enabled()).Times(AnyNumber());
+  EXPECT_CALL(*request_timer, enableTimer(kMessageTimeout, nullptr));
   EXPECT_CALL(stream_delegate_, send(_, false));
   sendRequestHeadersGet(true);
   EXPECT_CALL(decoder_callbacks_, continueDecoding());
+  EXPECT_CALL(*request_timer, disableTimer());
   sendRequestHeadersReply();
 
+  MockTimer* response_timer = new MockTimer(&dispatcher_);
+  EXPECT_CALL(*response_timer, enableTimer(kMessageTimeout, nullptr));
+  EXPECT_CALL(*response_timer, enabled()).Times(AnyNumber());
   EXPECT_CALL(stream_delegate_, send(_, false));
   sendResponseHeaders(true);
   EXPECT_CALL(encoder_callbacks_, sendLocalReply(Http::Code::InternalServerError, _, _, _, _));
+  EXPECT_CALL(*response_timer, disableTimer());
   sendImmediateResponse500();
   Buffer::OwnedImpl resp_body("Hello!");
   EXPECT_EQ(FilterDataStatus::Continue, filter_->encodeData(resp_body, true));