diff --git a/changes/bug21415 b/changes/bug21415
new file mode 100644
index 000000000..f0aa72f81
--- /dev/null
+++ b/changes/bug21415
@@ -0,0 +1,4 @@
+  o Minor bugfix (entry guards):
+    - Silence a BUG() warning when attempting to use a guard whose descriptor
+      we don't know and make this scenario more unlikely to happen. Fixes bug
+      21415; bugfix on 0.3.0.1-alpha.
diff --git a/src/or/entrynodes.c b/src/or/entrynodes.c
index 3e871477b..729e4b039 100644
--- a/src/or/entrynodes.c
+++ b/src/or/entrynodes.c
@@ -1843,7 +1843,7 @@ select_entry_guard_for_circuit(guard_selection_t *gs,
     if (! entry_guard_obeys_restriction(guard, rst))
       continue;
     if (guard->is_reachable != GUARD_REACHABLE_NO) {
-      if (need_descriptor && BUG(!guard_has_descriptor(guard))) {
+      if (need_descriptor && !guard_has_descriptor(guard)) {
         continue;
       }
       *state_out = GUARD_CIRC_STATE_USABLE_ON_COMPLETION;
@@ -3357,9 +3357,15 @@ guard_selection_have_enough_dir_info_to_build_circuits(guard_selection_t *gs)
   if (!gs->primary_guards_up_to_date)
     entry_guards_update_primary(gs);
 
-  const int num_primary = get_n_primary_guards_to_use(GUARD_USAGE_TRAFFIC);
   int n_missing_descriptors = 0;
   int n_considered = 0;
+  int num_primary_to_check;
+
+  /* We want to check for the descriptor of at least the first two primary
+   * guards in our list, since these are the guards that we typically use for
+   * circuits. */
+  num_primary_to_check = get_n_primary_guards_to_use(GUARD_USAGE_TRAFFIC);
+  num_primary_to_check++;
 
   SMARTLIST_FOREACH_BEGIN(gs->primary_entry_guards, entry_guard_t *, guard) {
     entry_guard_consider_retry(guard);
@@ -3368,7 +3374,7 @@ guard_selection_have_enough_dir_info_to_build_circuits(guard_selection_t *gs)
     n_considered++;
     if (!guard_has_descriptor(guard))
       n_missing_descriptors++;
-    if (n_considered >= num_primary)
+    if (n_considered >= num_primary_to_check)
       break;
   } SMARTLIST_FOREACH_END(guard);