2 files changed, 5 insertions, 0 deletions
diff --git a/source/core/slang-writer.cpp b/source/core/slang-writer.cpp
index 3b1a5756a..849cb2da0 100644
--- a/source/core/slang-writer.cpp
+++ b/source/core/slang-writer.cpp
@@ -71,6 +71,7 @@ ISlangUnknown* BaseWriter::getInterface(const Guid& guid)
 
 SLANG_NO_THROW char* SLANG_MCALL AppendBufferWriter::beginAppendBuffer(size_t maxNumChars)
 {
+    mutex.lock();
     m_appendBuffer.setCount(maxNumChars);
     return m_appendBuffer.getBuffer();
 }
@@ -82,6 +83,7 @@ SLANG_NO_THROW SlangResult SLANG_MCALL AppendBufferWriter::endAppendBuffer(char*
     SlangResult res = write(buffer, numChars);
     // Clear so that buffer can't be written from again without assert
     m_appendBuffer.clear();
+    mutex.unlock();
     return res;
 }
 
diff --git a/source/core/slang-writer.h b/source/core/slang-writer.h
index 7c768a22f..ccdcb3747 100644
--- a/source/core/slang-writer.h
+++ b/source/core/slang-writer.h
@@ -8,6 +8,8 @@
 
 #include "slang-list.h"
 
+#include <mutex>
+
 namespace Slang
 {
 
@@ -81,6 +83,7 @@ public:
 
 protected:
     List<char> m_appendBuffer;
+    std::mutex mutex;
 };
 
 class CallbackWriter : public AppendBufferWriter