diff --git a/src/modules/module-rtp/audio.c b/src/modules/module-rtp/audio.c
index 18dd9d0ee..1563e1917 100644
--- a/src/modules/module-rtp/audio.c
+++ b/src/modules/module-rtp/audio.c
@@ -376,7 +376,7 @@ static void set_timer(struct impl *impl, uint64_t time, uint64_t itime)
 	ts.it_interval.tv_nsec = itime % SPA_NSEC_PER_SEC;
 	spa_system_timerfd_settime(impl->data_loop->system,
 			impl->timer->fd, SPA_FD_TIMER_ABSTIME, &ts, NULL);
-	impl->timer_running = time != 0 && itime != 0;
+	set_timer_running(impl, time != 0 && itime != 0);
 }
 
 static void rtp_audio_flush_packets(struct impl *impl, uint32_t num_packets, uint64_t set_timestamp)
@@ -448,7 +448,7 @@ static void rtp_audio_flush_packets(struct impl *impl, uint32_t num_packets, uin
 	spa_ringbuffer_read_update(&impl->ring, timestamp);
 
 done:
-	if (impl->timer_running) {
+	if (is_timer_running(impl)) {
 		if (get_internal_stream_state(impl) != RTP_STREAM_INTERNAL_STATE_STOPPING) {
 			/* If the stream isn't being stopped, and instead is running,
 			 * keep the timer running if there was sufficient data to
diff --git a/src/modules/module-rtp/stream.c b/src/modules/module-rtp/stream.c
index f83019a3e..bb9da4995 100644
--- a/src/modules/module-rtp/stream.c
+++ b/src/modules/module-rtp/stream.c
@@ -141,7 +141,14 @@ struct impl {
 	struct pw_loop *main_loop;
 	struct pw_loop *data_loop;
 	struct spa_source *timer;
-	bool timer_running;
+	/* IMPORTANT: Do NOT access this value directly. Use the atomic
+	 * set_timer_running() / is_timer_running() accessors, since the
+	 * flag is accessed by both the dataloop and mainloop. To prevent
+	 * memory visibility issues, atomic accessors need to be used.
+	 *
+	 * Also, its type here is uint8_t. See the explanation about atomic
+	 * access below for the reason why. */
+	uint8_t timer_running;
 
 	int (*receive_rtp)(struct impl *impl, uint8_t *buffer, ssize_t len);
 	/* Used for resetting the ring buffer before the stream starts, to prevent
@@ -208,6 +215,21 @@ static inline void set_internal_stream_state(struct impl *impl, enum rtp_stream_
 	SPA_ATOMIC_STORE(impl->internal_state, (uint32_t)state);
 }
 
+/* Similar to the atomic internal_state accessors, these safeguard
+ * the timer_running flag, which can be accessed both by stream_stop()
+ * and the flush_timeout, which are called in separate threads.
+ * Since timer_running and internal_state are accessed independently,
+ * they are treated as two independent atomic variables instead of two
+ * resources under a common mutex. */
+
+static inline bool is_timer_running(struct impl *impl) {
+	return (bool)SPA_ATOMIC_LOAD(impl->timer_running);
+}
+
+static inline void set_timer_running(struct impl *impl, bool running) {
+	SPA_ATOMIC_STORE(impl->timer_running, (uint8_t)(running ? 1 : 0));
+}
+
 static int do_finish_stopping_state(struct spa_loop *loop, bool async, uint32_t seq, const void *data, size_t size, void *user_data)
 {
 	int res = 0;
@@ -381,6 +403,8 @@ static int stream_start(struct impl *impl)
 
 static int stream_stop(struct impl *impl)
 {
+	bool timer_running;
+
 	switch (get_internal_stream_state(impl)) {
 		case RTP_STREAM_INTERNAL_STATE_STOPPING:
 		case RTP_STREAM_INTERNAL_STATE_STOPPED:
@@ -391,10 +415,12 @@ static int stream_stop(struct impl *impl)
 
 	set_internal_stream_state(impl, RTP_STREAM_INTERNAL_STATE_STOPPING);
 
+	timer_running = is_timer_running(impl);
+
 	/* Proper stop is only possible if the timer is currently not running,
 	 * because a stop involves closing the connection. If the timer is still
 	 * running, it needs an open connection for sending out remaining packets. */
-	if (!impl->timer_running) {
+	if (!timer_running) {
 		int res;
 		pw_log_info("closing connection as part of stopping the stream");
 		rtp_stream_emit_close_connection(impl, &res);
@@ -422,7 +448,7 @@ static int stream_stop(struct impl *impl)
 	/* Only switch to STOPPED if the stream could _actually_ be stopped,
 	 * meaning that the timer was no longer running, and the connection
 	 * could be closed. */
-	if (!impl->timer_running) {
+	if (!timer_running) {
 		set_internal_stream_state(impl, RTP_STREAM_INTERNAL_STATE_STOPPED);
 		pw_log_info("stream stopped");
 	}