diff --git a/changes/bug3327 b/changes/bug3327
index 32a8b9cd02..454eb3156c 100644
--- a/changes/bug3327
+++ b/changes/bug3327
@@ -6,3 +6,9 @@
       to re-publish itself because it has done so too recently, even
       though the authorities decided not to list its recent-enough
       descriptor. Fix for bug 3327.
+
+  o Minor features:
+    - Relays now include a reason for regenerating their descriptors
+      an HTTP header when uploading to the authorities.  This will
+      make it easier to debug descriptor-upload issues in the future.
+
diff --git a/src/or/directory.c b/src/or/directory.c
index 6055ae38dd..f56a63c08c 100644
--- a/src/or/directory.c
+++ b/src/or/directory.c
@@ -1228,12 +1228,18 @@ directory_send_command(dir_connection_t *conn,
       httpcommand = "GET";
       tor_asprintf(&url, "/tor/micro/%s", resource);
       break;
-    case DIR_PURPOSE_UPLOAD_DIR:
+    case DIR_PURPOSE_UPLOAD_DIR: {
+      const char *why = router_get_descriptor_gen_reason();
       tor_assert(!resource);
       tor_assert(payload);
       httpcommand = "POST";
       url = tor_strdup("/tor/");
+      if (why) {
+        tor_asprintf(&header, "X-Desc-Gen-Reason: %s\r\n", why);
+        smartlist_add(headers, header);
+      }
       break;
+    }
     case DIR_PURPOSE_UPLOAD_VOTE:
       tor_assert(!resource);
       tor_assert(payload);
diff --git a/src/or/router.c b/src/or/router.c
index ccaa1398fd..07a65999bd 100644
--- a/src/or/router.c
+++ b/src/or/router.c
@@ -1220,9 +1220,14 @@ router_get_advertised_dir_port(const or_options_t *options, uint16_t dirport)
 static routerinfo_t *desc_routerinfo = NULL;
 /** My extrainfo */
 static extrainfo_t *desc_extrainfo = NULL;
+/** Why did we most recently decide to regenerate our descriptor?  Used to
+ * tell the authorities why we're sending it to them. */
+static const char *desc_gen_reason = NULL;
 /** Since when has our descriptor been "clean"?  0 if we need to regenerate it
  * now. */
 static time_t desc_clean_since = 0;
+/** Why did we mark the descriptor dirty? */
+static const char *desc_dirty_reason = NULL;
 /** Boolean: do we need to regenerate the above? */
 static int desc_needs_upload = 0;
 
@@ -1389,6 +1394,14 @@ router_get_my_extrainfo(void)
   return desc_extrainfo;
 }
 
+/** Return a human-readable string describing what triggered us to generate
+ * our current descriptor, or NULL if we don't know. */
+const char *
+router_get_descriptor_gen_reason(void)
+{
+  return desc_gen_reason;
+}
+
 /** A list of nicknames that we've warned about including in our family
  * declaration verbatim rather than as digests. */
 static smartlist_t *warned_nonexistent_family = NULL;
@@ -1606,6 +1619,8 @@ router_rebuild_descriptor(int force)
 
   desc_clean_since = time(NULL);
   desc_needs_upload = 1;
+  desc_gen_reason = desc_dirty_reason;
+  desc_dirty_reason = NULL;
   control_event_my_descriptor_changed();
   return 0;
 }
@@ -1662,6 +1677,8 @@ mark_my_descriptor_dirty(const char *reason)
 {
   desc_clean_since = 0;
   log_info(LD_OR, "Decided to publish new relay descriptor: %s", reason);
+  if (!desc_dirty_reason)
+    desc_dirty_reason = reason;
 }
 
 /** How frequently will we republish our descriptor because of large (factor
diff --git a/src/or/router.h b/src/or/router.h
index af202e60c4..f9d156cb09 100644
--- a/src/or/router.h
+++ b/src/or/router.h
@@ -73,6 +73,7 @@ int router_my_exit_policy_is_reject_star(void);
 const routerinfo_t *router_get_my_routerinfo(void);
 extrainfo_t *router_get_my_extrainfo(void);
 const char *router_get_my_descriptor(void);
+const char *router_get_descriptor_gen_reason(void);
 int router_digest_is_me(const char *digest);
 int router_extrainfo_digest_is_me(const char *digest);
 int router_is_me(const routerinfo_t *router);