diff --git a/image/IDecodingTask.h b/image/IDecodingTask.h
index 380e680950cf..f5e67545c8d4 100644
--- a/image/IDecodingTask.h
+++ b/image/IDecodingTask.h
@@ -88,7 +88,7 @@ class MetadataDecodingTask final : public IDecodingTask {
  * An IDecodingTask implementation for anonymous decoders - that is, decoders
  * with no associated Image object.
  */
-class AnonymousDecodingTask final : public IDecodingTask {
+class AnonymousDecodingTask : public IDecodingTask {
  public:
   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(AnonymousDecodingTask, override)
 
@@ -101,7 +101,7 @@ class AnonymousDecodingTask final : public IDecodingTask {
 
   void Resume() override;
 
- private:
+ protected:
   virtual ~AnonymousDecodingTask() {}
 
   NotNull<RefPtr<Decoder>> mDecoder;
diff --git a/image/test/gtest/TestDecoders.cpp b/image/test/gtest/TestDecoders.cpp
index f043b011d033..4b1f6cf2b6cc 100644
--- a/image/test/gtest/TestDecoders.cpp
+++ b/image/test/gtest/TestDecoders.cpp
@@ -5,6 +5,7 @@
 #include "gtest/gtest.h"
 
 #include "Common.h"
+#include "mozilla/Monitor.h"
 #include "AnimationSurfaceProvider.h"
 #include "DecodePool.h"
 #include "Decoder.h"
@@ -122,6 +123,67 @@ static void CheckDecoderBadBuffer(const ImageTestCase& aTestCase) {
   });
 }
 
+/**
+ * AnonymousDecodingTask but with a monitor so we can wait for it to finish
+ * safely.
+ */
+class MonitorAnonymousDecodingTask final : public AnonymousDecodingTask {
+ public:
+  explicit MonitorAnonymousDecodingTask(NotNull<Decoder*> aDecoder,
+                                        bool aResumable);
+
+  void Run() override;
+
+  void WaitUntilFinished();
+
+ private:
+  virtual ~MonitorAnonymousDecodingTask() = default;
+
+  Monitor mMonitor MOZ_UNANNOTATED;
+};
+
+MonitorAnonymousDecodingTask::MonitorAnonymousDecodingTask(
+    NotNull<Decoder*> aDecoder, bool aResumable)
+    : AnonymousDecodingTask(aDecoder, aResumable),
+      mMonitor("MonitorAnonymousDecodingTask") {}
+
+void MonitorAnonymousDecodingTask::Run() {
+  MonitorAutoLock lock(mMonitor);
+
+  while (true) {
+    LexerResult result = mDecoder->Decode(WrapNotNull(this));
+
+    if (result.is<TerminalState>()) {
+      mMonitor.NotifyAll();
+      return;  // We're done.
+    }
+
+    if (result == LexerResult(Yield::NEED_MORE_DATA)) {
+      // We can't make any more progress right now. Let the caller decide how to
+      // handle it.
+      mMonitor.NotifyAll();
+      return;
+    }
+
+    // Right now we don't do anything special for other kinds of yields, so just
+    // keep working.
+    MOZ_ASSERT(result.is<Yield>());
+  }
+}
+
+void MonitorAnonymousDecodingTask::WaitUntilFinished() {
+  MonitorAutoLock lock(mMonitor);
+
+  while (true) {
+    if (mDecoder->GetDecodeDone()) {
+      return;
+    }
+
+    // Not done yet, so we'll have to wait.
+    mMonitor.Wait();
+  }
+}
+
 template <typename Func>
 void WithSingleChunkDecode(const ImageTestCase& aTestCase,
                            const Maybe<IntSize>& aOutputSize,
@@ -150,15 +212,13 @@ void WithSingleChunkDecode(const ImageTestCase& aTestCase,
       decoderType, sourceBuffer, aOutputSize, decoderFlags,
       aTestCase.mSurfaceFlags);
   ASSERT_TRUE(decoder != nullptr);
-  RefPtr<IDecodingTask> task =
-      new AnonymousDecodingTask(WrapNotNull(decoder), /* aResumable */ false);
+  RefPtr<MonitorAnonymousDecodingTask> task = new MonitorAnonymousDecodingTask(
+      WrapNotNull(decoder), /* aResumable */ false);
 
   if (aUseDecodePool) {
     DecodePool::Singleton()->AsyncRun(task.get());
 
-    while (!decoder->GetDecodeDone()) {
-      task->Resume();
-    }
+    task->WaitUntilFinished();
   } else {  // Run the full decoder synchronously on the main thread.
     task->Run();
   }
diff --git a/image/test/gtest/moz.build b/image/test/gtest/moz.build
index 2501e98f60d2..9ab29ceb2e66 100644
--- a/image/test/gtest/moz.build
+++ b/image/test/gtest/moz.build
@@ -12,6 +12,7 @@ UNIFIED_SOURCES = [
     "TestAnimationFrameBuffer.cpp",
     "TestBlendAnimationFilter.cpp",
     "TestCopyOnWrite.cpp",
+    "TestDecoders.cpp",
     "TestDecodersPerf.cpp",
     "TestDecodeToSurface.cpp",
     "TestDeinterlacingFilter.cpp",
@@ -28,12 +29,6 @@ UNIFIED_SOURCES = [
     "TestSwizzleFilter.cpp",
 ]
 
-# Bug 1894284 - Fails under TSAN
-if not CONFIG["MOZ_TSAN"]:
-    UNIFIED_SOURCES += [
-        "TestDecoders.cpp",
-    ]
-
 TEST_HARNESS_FILES.gtest += [
     "animated-with-extra-image-sub-blocks.gif",
     "blend.avif",