diff --git a/core-writer/src/RingBuffer.cpp b/core-writer/src/RingBuffer.cpp
index 3b046ba..11978b6 100644
--- a/core-writer/src/RingBuffer.cpp
+++ b/core-writer/src/RingBuffer.cpp
@@ -69,9 +69,14 @@ void RingBuffer::initialize(size_t slot_size)
 
 char* RingBuffer::reserve(shared_ptr<FrameMetadata> frame_metadata)
 {
-    // TODO: Synchronize this as well.
     if (!ring_buffer_initialized_) {
-        initialize(frame_metadata->frame_bytes_size);
+        {
+            lock_guard<mutex> lock(ringbuffer_slots_mutex_);
+
+            if (!ring_buffer_initialized_) {
+                initialize(frame_metadata->frame_bytes_size);
+            }
+        }
     }
 
     if (frame_metadata->frame_bytes_size > slot_size_) {