diff --git a/gc/gc.h b/gc/gc.h
index 05f7e87..69e0e0b 100644
--- a/gc/gc.h
+++ b/gc/gc.h
@@ -194,6 +194,14 @@ gc_mark_tbl_no_pin_i(st_data_t key, st_data_t value, st_data_t data)
     return ST_CONTINUE;
 }
 
+static int
+gc_mark_set_no_pin_i(st_data_t key, st_data_t value, st_data_t data)
+{
+    rb_gc_mark_movable((VALUE)key);
+
+    return ST_CONTINUE;
+}
+
 static int
 hash_foreach_replace(st_data_t key, st_data_t value, st_data_t argp, int error)
 {
@@ -232,6 +240,36 @@ gc_update_table_refs(st_table *tbl)
     }
 }
 
+static int
+rb_set_foreach_replace(st_data_t key, st_data_t value, st_data_t argp, int error)
+{
+    if (rb_gc_location((VALUE)key) != (VALUE)key) {
+        return ST_REPLACE;
+    }
+
+    return ST_CONTINUE;
+}
+
+static int
+rb_set_replace_ref(st_data_t *key, st_data_t *value, st_data_t argp, int existing)
+{
+    if (rb_gc_location((VALUE)*key) != (VALUE)*key) {
+        *key = rb_gc_location((VALUE)*key);
+    }
+
+    return ST_CONTINUE;
+}
+
+static void
+gc_update_set_refs(st_table *tbl)
+{
+    if (!tbl || tbl->num_entries == 0) return;
+
+    if (st_foreach_with_replace(tbl, rb_set_foreach_replace, rb_set_replace_ref, 0)) {
+        rb_raise(rb_eRuntimeError, "hash modified during iteration");
+    }
+}
+
 static inline size_t
 xmalloc2_size(const size_t count, const size_t elsize)
 {
diff --git a/gc/mmtk/mmtk.c b/gc/mmtk/mmtk.c
index 24f0567..96e9e32 100644
--- a/gc/mmtk/mmtk.c
+++ b/gc/mmtk/mmtk.c
@@ -475,6 +475,7 @@ rb_mmtk_special_const_p(MMTk_ObjectReference object)
 }
 
 RBIMPL_ATTR_FORMAT(RBIMPL_PRINTF_FORMAT, 1, 2)
+RBIMPL_ATTR_NORETURN()
 static void
 rb_mmtk_gc_thread_bug(const char *msg, ...)
 {
@@ -505,6 +506,7 @@ rb_mmtk_gc_thread_panic_handler(void)
     rb_mmtk_gc_thread_bug("MMTk GC thread panicked");
 }
 
+RBIMPL_ATTR_NORETURN()
 static void
 rb_mmtk_mutator_thread_panic_handler(void)
 {