diff --git a/ultramodern/src/mesgqueue.cpp b/ultramodern/src/mesgqueue.cpp
index 9944a02..7714b8f 100644
--- a/ultramodern/src/mesgqueue.cpp
+++ b/ultramodern/src/mesgqueue.cpp
@@ -1,3 +1,4 @@
+#include <atomic>
 #include <bitset>
 #include <thread>
 
@@ -16,6 +17,18 @@ struct QueuedMessage {
 static moodycamel::BlockingConcurrentQueue<QueuedMessage> external_messages {};
 std::bitset<32> requeue_enabled;
 
+// Counter for how many external messages have been re-queued because
+// their target OSMesgQueue was full at dequeue time. Bumped at the
+// three requeue sites in dequeue_external_messages,
+// wait_for_external_message, and wait_for_external_message_timed. A
+// sustained nonzero rate indicates a target queue is being overrun
+// (receiver thread starved); useful for runner-side observability.
+static std::atomic<uint64_t> g_external_requeues{0};
+
+extern "C" uint64_t ultramodern_external_requeues(void) {
+    return g_external_requeues.load(std::memory_order_relaxed);
+}
+
 void ultramodern::set_message_queue_control(const ultramodern::MessageQueueControl& mqc) {
     requeue_enabled.reset();
     requeue_enabled.set(static_cast<int>(EventMessageSource::Timer), mqc.requeue_timer);
@@ -45,8 +58,11 @@ void dequeue_external_messages(RDRAM_ARG1) {
             requeued_messages.push_back(to_send);
         }
     }
-    for (QueuedMessage& cur_mesg : requeued_messages) {
-        external_messages.enqueue(cur_mesg);
+    if (!requeued_messages.empty()) {
+        g_external_requeues.fetch_add(requeued_messages.size(), std::memory_order_relaxed);
+        for (QueuedMessage& cur_mesg : requeued_messages) {
+            external_messages.enqueue(cur_mesg);
+        }
     }
 }
 
@@ -54,6 +70,7 @@ void ultramodern::wait_for_external_message(RDRAM_ARG1) {
     QueuedMessage to_send;
     external_messages.wait_dequeue(to_send);
     if (!do_send(PASS_RDRAM to_send.mq, to_send.mesg, to_send.jam, false) && to_send.requeue_if_blocked) {
+        g_external_requeues.fetch_add(1, std::memory_order_relaxed);
         external_messages.enqueue(to_send);
     }
 }
@@ -62,6 +79,7 @@ void ultramodern::wait_for_external_message_timed(RDRAM_ARG u32 millis) {
     QueuedMessage to_send;
     if (external_messages.wait_dequeue_timed(to_send, std::chrono::milliseconds{millis})) {
         if (!do_send(PASS_RDRAM to_send.mq, to_send.mesg, to_send.jam, false) && to_send.requeue_if_blocked) {
+            g_external_requeues.fetch_add(1, std::memory_order_relaxed);
             external_messages.enqueue(to_send);
         }
     }