diff --git a/lldb/include/lldb/Utility/ReproducerInstrumentation.h b/lldb/include/lldb/Utility/ReproducerInstrumentation.h
--- a/lldb/include/lldb/Utility/ReproducerInstrumentation.h
+++ b/lldb/include/lldb/Utility/ReproducerInstrumentation.h
@@ -868,17 +868,14 @@
 
   /// Mark the current thread as a private thread and pretend that everything
   /// on this thread is behind happening behind the API boundary.
-  static void PrivateThread() { g_global_boundary = true; }
+  static void PrivateThread();
 
 private:
   static unsigned GetNextSequenceNumber() { return g_sequence++; }
   unsigned GetSequenceNumber() const;
 
   template <typename T> friend struct replay;
-  void UpdateBoundary() {
-    if (m_local_boundary)
-      g_global_boundary = false;
-  }
+  void UpdateBoundary();
 
 #ifdef LLDB_REPRO_INSTR_TRACE
   void Log(unsigned id) {
@@ -902,9 +899,6 @@
   /// The sequence number for this pair of function and result.
   unsigned m_sequence;
 
-  /// Whether we're currently across the API boundary.
-  static thread_local bool g_global_boundary;
-
   /// Global mutex to protect concurrent access.
   static std::mutex g_mutex;
 
diff --git a/lldb/source/Utility/ReproducerInstrumentation.cpp b/lldb/source/Utility/ReproducerInstrumentation.cpp
--- a/lldb/source/Utility/ReproducerInstrumentation.cpp
+++ b/lldb/source/Utility/ReproducerInstrumentation.cpp
@@ -16,6 +16,9 @@
 using namespace lldb_private;
 using namespace lldb_private::repro;
 
+// Whether we're currently across the API boundary.
+static thread_local bool g_global_boundary = false;
+
 void *IndexToObject::GetObjectForIndexImpl(unsigned idx) {
   return m_mapping.lookup(idx);
 }
@@ -227,6 +230,13 @@
   return m_sequence;
 }
 
+void Recorder::PrivateThread() { g_global_boundary = true; }
+
+void Recorder::UpdateBoundary() {
+  if (m_local_boundary)
+    g_global_boundary = false;
+}
+
 void InstrumentationData::Initialize(Serializer &serializer,
                                      Registry &registry) {
   InstanceImpl().emplace(serializer, registry);
@@ -248,6 +258,5 @@
   return g_instrumentation_data;
 }
 
-thread_local bool lldb_private::repro::Recorder::g_global_boundary = false;
 std::atomic<unsigned> lldb_private::repro::Recorder::g_sequence;
 std::mutex lldb_private::repro::Recorder::g_mutex;