diff --git a/include/shader-debug/debug_channel.h b/include/shader-debug/debug_channel.h
index 7e76c852..97e3b2ab 100644
--- a/include/shader-debug/debug_channel.h
+++ b/include/shader-debug/debug_channel.h
@@ -51,6 +51,7 @@ const uint DEBUG_CHANNEL_FMT_F32 = 2;
 const uint DEBUG_CHANNEL_FMT_HEX_ALL = DEBUG_CHANNEL_FMT_HEX * 0x55555555u;
 const uint DEBUG_CHANNEL_FMT_I32_ALL = DEBUG_CHANNEL_FMT_I32 * 0x55555555u;
 const uint DEBUG_CHANNEL_FMT_F32_ALL = DEBUG_CHANNEL_FMT_F32 * 0x55555555u;
+const uint DEBUG_CHANNEL_WORD_COOKIE = 0xdeadca70u; /* Let host fish for this cookie in device lost scenarios. */
 
 uint DEBUG_CHANNEL_INSTANCE_COUNTER;
 uvec3 DEBUG_CHANNEL_ID;
@@ -103,7 +104,7 @@ void DEBUG_CHANNEL_UNLOCK_MESSAGE(RingBuffer buf, uint offset, uint num_words)
 	 * If the host thread observed a num_word of 0, we know a message was allocated, but we don't necessarily
 	 * have a complete write yet.
 	 * In a device lost scenario, we can try to fish for valid messages. */
-	buf.data[(offset + 0) & DEBUG_SHADER_RING_MASK] = num_words;
+	buf.data[(offset + 0) & DEBUG_SHADER_RING_MASK] = num_words | DEBUG_CHANNEL_WORD_COOKIE;
 	memoryBarrierBuffer();
 }
 
diff --git a/libs/vkd3d/debug_ring.c b/libs/vkd3d/debug_ring.c
index c63b0092..53848d0e 100644
--- a/libs/vkd3d/debug_ring.c
+++ b/libs/vkd3d/debug_ring.c
@@ -104,6 +104,8 @@ void *vkd3d_shader_debug_ring_thread_main(void *arg)
                 /* The debug ring shader has "release" semantics for the word count write,
                  * so just make sure the reads don't get reordered here. */
                 message_word_count = READ_RING_WORD_ACQUIRE(0);
+#define DEBUG_CHANNEL_WORD_COOKIE 0xdeadca70u
+#define DEBUG_CHANNEL_WORD_MASK 0xfffffff0u
 
                 if (message_word_count == 0)
                 {
@@ -114,6 +116,15 @@ void *vkd3d_shader_debug_ring_thread_main(void *arg)
                     break;
                 }
 
+                /* If something is written here, it must be a cookie. */
+                if ((message_word_count & DEBUG_CHANNEL_WORD_MASK) != DEBUG_CHANNEL_WORD_COOKIE)
+                {
+                    ERR("Invalid message work cookie detected, 0x%x.\n", message_word_count);
+                    break;
+                }
+
+                message_word_count &= ~DEBUG_CHANNEL_WORD_MASK;
+
                 if (i + message_word_count > count)
                 {
                     ERR("Message word count %u is out of bounds (i = %u, count = %u).\n",
@@ -121,7 +132,7 @@ void *vkd3d_shader_debug_ring_thread_main(void *arg)
                     break;
                 }
 
-                if (message_word_count < 8 || message_word_count > 16 + 8)
+                if (message_word_count < 8)
                 {
                     ERR("Message word count %u is invalid.\n", message_word_count);
                     break;