diff --git a/ipc/chromium/src/base/pickle.cc b/ipc/chromium/src/base/pickle.cc
index 6e6a9804b182..cf30bd2e51eb 100644
--- a/ipc/chromium/src/base/pickle.cc
+++ b/ipc/chromium/src/base/pickle.cc
@@ -24,7 +24,14 @@
 static_assert(MOZ_ALIGNOF(Pickle::memberAlignmentType) >= MOZ_ALIGNOF(uint32_t),
               "Insufficient alignment");
 
+#ifndef MOZ_TASK_TRACER
 static const uint32_t kHeaderSegmentCapacity = 64;
+#else
+// TaskTracer would add extra fields to the header to carry task ID and
+// other information.
+// \see class Message::HeaderTaskTracer
+static const uint32_t kHeaderSegmentCapacity = 128;
+#endif
 
 static const uint32_t kDefaultSegmentCapacity = 4096;
 
diff --git a/mfbt/BufferList.h b/mfbt/BufferList.h
index 42aea12dbc05..2bb9bb7e01d8 100644
--- a/mfbt/BufferList.h
+++ b/mfbt/BufferList.h
@@ -316,6 +316,7 @@ private:
   void* AllocateSegment(size_t aSize, size_t aCapacity)
   {
     MOZ_RELEASE_ASSERT(mOwning);
+    MOZ_ASSERT(aSize <= aCapacity);
 
     char* data = this->template pod_malloc<char>(aCapacity);
     if (!data) {