diff --git a/include/haproxy/tinfo-t.h b/include/haproxy/tinfo-t.h
index 991786fc2..8aff35452 100644
--- a/include/haproxy/tinfo-t.h
+++ b/include/haproxy/tinfo-t.h
@@ -64,6 +64,7 @@ enum {
 #define TH_FL_SLEEPING          0x00000008  /* thread won't check its task list before next wakeup */
 #define TH_FL_STARTED           0x00000010  /* set once the thread starts */
 #define TH_FL_IN_LOOP           0x00000020  /* set only inside the polling loop */
+#define TH_FL_DUMPING_OTHERS    0x00000040  /* thread currently dumping other threads */
 
 /* we have 4 buffer-wait queues, in highest to lowest emergency order */
 #define DYNBUF_NBQ              4
diff --git a/src/debug.c b/src/debug.c
index 61254ba4e..35f60c7a4 100644
--- a/src/debug.c
+++ b/src/debug.c
@@ -358,12 +358,23 @@ void ha_thread_dump_one(int thr, int from_signal)
  * there is enough room otherwise some contents will be truncated. The function
  * waits for the called thread to fill the buffer before returning (or cancelling
  * by reporting NULL). It does not release the called thread yet. It returns a
- * pointer to the buffer used if the dump was done, otherwise NULL.
+ * pointer to the buffer used if the dump was done, otherwise NULL. When the
+ * dump starts, it marks the current thread as dumping, which will only be
+ * released via a failure (returns NULL) or via a call to ha_dump_thread_done().
  */
 struct buffer *ha_thread_dump_fill(struct buffer *buf, int thr)
 {
 	struct buffer *old = NULL;
 
+	/* A thread that's currently dumping other threads cannot be dumped, or
+	 * it will very likely cause a deadlock.
+	 */
+	if (HA_ATOMIC_LOAD(&ha_thread_ctx[thr].flags) & TH_FL_DUMPING_OTHERS)
+		return NULL;
+
+	/* This will be undone in ha_thread_dump_done() */
+	HA_ATOMIC_OR(&th_ctx->flags, TH_FL_DUMPING_OTHERS);
+
 	/* try to impose our dump buffer and to reserve the target thread's
 	 * next dump for us.
 	 */
@@ -388,8 +399,11 @@ struct buffer *ha_thread_dump_fill(struct buffer *buf, int thr)
 		old = HA_ATOMIC_LOAD(&ha_thread_ctx[thr].thread_dump_buffer);
 		if ((ulong)old & 0x1)
 			break;
-		if (!old)
+		if (!old) {
+			/* cancelled: no longer dumping */
+			HA_ATOMIC_AND(&th_ctx->flags, ~TH_FL_DUMPING_OTHERS);
 			return old;
+		}
 		ha_thread_relax();
 	}
 	return (struct buffer *)((ulong)old & ~0x1UL);
@@ -409,11 +423,13 @@ void ha_thread_dump_done(struct buffer *buf, int thr)
 		old = HA_ATOMIC_LOAD(&ha_thread_ctx[thr].thread_dump_buffer);
 		if (!((ulong)old & 0x1)) {
 			if (!old)
-				return;
+				break;
 			ha_thread_relax();
 			continue;
 		}
 	} while (!HA_ATOMIC_CAS(&ha_thread_ctx[thr].thread_dump_buffer, &old, buf));
+
+	HA_ATOMIC_AND(&th_ctx->flags, ~TH_FL_DUMPING_OTHERS);
 }
 
 /* dumps into the buffer some information related to task <task> (which may
diff --git a/src/haproxy.c b/src/haproxy.c
index 3f5b9db09..52ee3dbd2 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -2749,6 +2749,9 @@ void run_poll_loop()
 		/* Process a few tasks */
 		process_runnable_tasks();
 
+		/* If this happens this is an accidental leak */
+		BUG_ON(HA_ATOMIC_LOAD(&th_ctx->flags) & TH_FL_DUMPING_OTHERS);
+
 		/* also stop  if we failed to cleanly stop all tasks */
 		if (killed > 1)
 			break;
diff --git a/src/wdt.c b/src/wdt.c
index 2a9e41605..dd8f9a1a4 100644
--- a/src/wdt.c
+++ b/src/wdt.c
@@ -95,13 +95,15 @@ void wdt_handler(int sig, siginfo_t *si, void *arg)
 		if (!p)
 			goto update_and_leave;
 
-		if ((_HA_ATOMIC_LOAD(&ha_thread_ctx[thr].flags) & TH_FL_SLEEPING) ||
+		if ((_HA_ATOMIC_LOAD(&ha_thread_ctx[thr].flags) & (TH_FL_SLEEPING|TH_FL_DUMPING_OTHERS)) ||
 		    (_HA_ATOMIC_LOAD(&ha_tgroup_ctx[tgrp-1].threads_harmless) & thr_bit)) {
 			/* This thread is currently doing exactly nothing
 			 * waiting in the poll loop (unlikely but possible),
 			 * waiting for all other threads to join the rendez-vous
 			 * point (common), or waiting for another thread to
-			 * finish an isolated operation (unlikely but possible).
+			 * finish an isolated operation (unlikely but possible),
+			 * or waiting for another thread to finish dumping its
+			 * stack.
 			 */
 			goto update_and_leave;
 		}