diff --git a/ddprof-lib/src/main/cpp/flightRecorder.cpp b/ddprof-lib/src/main/cpp/flightRecorder.cpp
index 3b788efc1..794e45ed7 100644
--- a/ddprof-lib/src/main/cpp/flightRecorder.cpp
+++ b/ddprof-lib/src/main/cpp/flightRecorder.cpp
@@ -1699,9 +1699,11 @@ void Recording::writeContextSnapshot(Buffer *buf, Context &context) {
 void Recording::writeCurrentContext(Buffer *buf) {
   u64 spanId = 0;
   u64 rootSpanId = 0;
-  bool hasContext = ContextApi::get(spanId, rootSpanId);
   // spanId/rootSpanId are initialized to 0 above; ContextApi::get() only updates them
-  // on success, so 0s are always written when there is no valid context.
+  // on success, so 0s are always written when there is no active span.
+  // hasContext gates sidecar reads: getOtelTagEncoding() must only be called
+  // when valid=1 (see thread.h read invariant).
+  bool hasContext = ContextApi::get(spanId, rootSpanId);
   buf->putVar64(spanId);
   buf->putVar64(rootSpanId);