diff --git a/dom/base/nsStructuredCloneContainer.cpp b/dom/base/nsStructuredCloneContainer.cpp
index 27111666c41f..970b1ce695a1 100644
--- a/dom/base/nsStructuredCloneContainer.cpp
+++ b/dom/base/nsStructuredCloneContainer.cpp
@@ -130,7 +130,9 @@ nsStructuredCloneContainer::GetDataAsBase64(nsAString& aOut) {
   size_t size = Data().Size();
   nsAutoCString binaryData;
   binaryData.SetLength(size);
-  Data().ReadBytes(iter, binaryData.BeginWriting(), size);
+  if (!Data().ReadBytes(iter, binaryData.BeginWriting(), size)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
   nsAutoCString base64Data;
   nsresult rv = Base64Encode(binaryData, base64Data);
   if (NS_WARN_IF(NS_FAILED(rv))) {
diff --git a/dom/ipc/StructuredCloneData.h b/dom/ipc/StructuredCloneData.h
index c140d3076293..bac00e9aa473 100644
--- a/dom/ipc/StructuredCloneData.h
+++ b/dom/ipc/StructuredCloneData.h
@@ -52,7 +52,7 @@ class SharedJSAllocatedData final {
   static already_AddRefed<SharedJSAllocatedData> CreateFromExternalData(
       const char* aData, size_t aDataLength) {
     JSStructuredCloneData buf(JS::StructuredCloneScope::DifferentProcess);
-    buf.AppendBytes(aData, aDataLength);
+    NS_ENSURE_TRUE(buf.AppendBytes(aData, aDataLength), nullptr);
     RefPtr<SharedJSAllocatedData> sharedData =
         new SharedJSAllocatedData(std::move(buf));
     return sharedData.forget();
@@ -61,7 +61,7 @@ class SharedJSAllocatedData final {
   static already_AddRefed<SharedJSAllocatedData> CreateFromExternalData(
       const JSStructuredCloneData& aData) {
     JSStructuredCloneData buf(aData.scope());
-    buf.Append(aData);
+    NS_ENSURE_TRUE(buf.Append(aData), nullptr);
     RefPtr<SharedJSAllocatedData> sharedData =
         new SharedJSAllocatedData(std::move(buf));
     return sharedData.forget();
diff --git a/ipc/glue/IPCMessageUtils.h b/ipc/glue/IPCMessageUtils.h
index 9d0768381310..aeff61c75844 100644
--- a/ipc/glue/IPCMessageUtils.h
+++ b/ipc/glue/IPCMessageUtils.h
@@ -84,7 +84,7 @@ struct SerializedStructuredCloneBuffer final {
       const SerializedStructuredCloneBuffer& aOther) {
     data.Clear();
     data.initScope(aOther.data.scope());
-    data.Append(aOther.data);
+    MOZ_RELEASE_ASSERT(data.Append(aOther.data), "out of memory");
     return *this;
   }
 
diff --git a/js/public/StructuredClone.h b/js/public/StructuredClone.h
index f6dbc2c501ac..847afe001076 100644
--- a/js/public/StructuredClone.h
+++ b/js/public/StructuredClone.h
@@ -439,7 +439,7 @@ class MOZ_NON_MEMMOVABLE JS_PUBLIC_API JSStructuredCloneData {
     ownTransferables_ = policy;
   }
 
-  bool Init(size_t initialCapacity = 0) {
+  MOZ_MUST_USE bool Init(size_t initialCapacity = 0) {
     return bufList_.Init(0, initialCapacity);
   }
 
@@ -458,23 +458,24 @@ class MOZ_NON_MEMMOVABLE JS_PUBLIC_API JSStructuredCloneData {
 
   const Iterator Start() const { return bufList_.Iter(); }
 
-  bool Advance(Iterator& iter, size_t distance) const {
+  MOZ_MUST_USE bool Advance(Iterator& iter, size_t distance) const {
     return iter.AdvanceAcrossSegments(bufList_, distance);
   }
 
-  bool ReadBytes(Iterator& iter, char* buffer, size_t size) const {
+  MOZ_MUST_USE bool ReadBytes(Iterator& iter, char* buffer, size_t size) const {
     return bufList_.ReadBytes(iter, buffer, size);
   }
 
   // Append new data to the end of the buffer.
-  bool AppendBytes(const char* data, size_t size) {
+  MOZ_MUST_USE bool AppendBytes(const char* data, size_t size) {
     MOZ_ASSERT(scope_ != JS::StructuredCloneScope::Unassigned);
     return bufList_.WriteBytes(data, size);
   }
 
   // Update data stored within the existing buffer. There must be at least
   // 'size' bytes between the position of 'iter' and the end of the buffer.
-  bool UpdateBytes(Iterator& iter, const char* data, size_t size) const {
+  MOZ_MUST_USE bool UpdateBytes(Iterator& iter, const char* data,
+                                size_t size) const {
     MOZ_ASSERT(scope_ != JS::StructuredCloneScope::Unassigned);
     while (size > 0) {
       size_t remaining = iter.RemainingInSegment();
@@ -524,7 +525,7 @@ class MOZ_NON_MEMMOVABLE JS_PUBLIC_API JSStructuredCloneData {
   }
 
   // Append the entire contents of other's bufList_ to our own.
-  bool Append(const JSStructuredCloneData& other) {
+  MOZ_MUST_USE bool Append(const JSStructuredCloneData& other) {
     MOZ_ASSERT(scope_ == other.scope());
     return other.ForEachDataChunk(
         [&](const char* data, size_t size) { return AppendBytes(data, size); });
diff --git a/js/src/builtin/TestingFunctions.cpp b/js/src/builtin/TestingFunctions.cpp
index c1ec55c282fb..d9a6344ce429 100644
--- a/js/src/builtin/TestingFunctions.cpp
+++ b/js/src/builtin/TestingFunctions.cpp
@@ -2944,7 +2944,10 @@ class CloneBufferObject : public NativeObject {
       return false;
     }
     auto iter = data->Start();
-    data->ReadBytes(iter, buffer.get(), size);
+    if (!data->ReadBytes(iter, buffer.get(), size)) {
+      ReportOutOfMemory(cx);
+      return false;
+    }
     JSString* str = JS_NewStringCopyN(cx, buffer.get(), size);
     if (!str) {
       return false;
@@ -2976,7 +2979,10 @@ class CloneBufferObject : public NativeObject {
       return false;
     }
     auto iter = data->Start();
-    data->ReadBytes(iter, buffer.get(), size);
+    if (!data->ReadBytes(iter, buffer.get(), size)) {
+      ReportOutOfMemory(cx);
+      return false;
+    }
 
     auto* rawBuffer = buffer.release();
     JSObject* arrayBuffer = JS::NewArrayBufferWithContents(cx, size, rawBuffer);
diff --git a/js/src/fuzz-tests/testStructuredCloneReader.cpp b/js/src/fuzz-tests/testStructuredCloneReader.cpp
index 0f8e92f15b8a..2bb5d9e4285b 100644
--- a/js/src/fuzz-tests/testStructuredCloneReader.cpp
+++ b/js/src/fuzz-tests/testStructuredCloneReader.cpp
@@ -44,9 +44,15 @@ static int testStructuredCloneReaderFuzz(const uint8_t* buf, size_t size) {
   }
 
   // Copy buffer then pad with zeroes.
-  clonebuf->AppendBytes((const char*)buf, size);
+  if (!clonebuf->AppendBytes((const char*)buf, size)) {
+    ReportOutOfMemory(gCx);
+    return 0;
+  }
   char padding[kSegmentAlignment] = {0};
-  clonebuf->AppendBytes(padding, buf_size - size);
+  if (!clonebuf->AppendBytes(padding, buf_size - size)) {
+    ReportOutOfMemory(gCx);
+    return 0;
+  }
 
   RootedValue deserialized(gCx);
   if (!JS_ReadStructuredClone(gCx, *clonebuf, JS_STRUCTURED_CLONE_VERSION,