diff --git a/st.c b/st.c
index f11e9efaf9..70da7daf83 100644
--- a/st.c
+++ b/st.c
@@ -1495,7 +1495,16 @@ st_update(st_table *tab, st_data_t key,
         value = entry->record;
     }
     old_key = key;
+
+    unsigned int rebuilds_num = tab->rebuilds_num;
+
     retval = (*func)(&key, &value, arg, existing);
+
+    // We need to make sure that the callback didn't cause a table rebuild
+    // Ideally we would make sure no operations happened
+    assert(rebuilds_num == tab->rebuilds_num);
+    (void)rebuilds_num;
+
     switch (retval) {
       case ST_CONTINUE:
         if (! existing) {
diff --git a/test/ruby/test_variable.rb b/test/ruby/test_variable.rb
index 49fec2d40e..d8d0a1a393 100644
--- a/test/ruby/test_variable.rb
+++ b/test/ruby/test_variable.rb
@@ -407,6 +407,19 @@ class TestVariable < Test::Unit::TestCase
     }
   end
 
+  def test_exivar_resize_with_compaction_stress
+    objs = 10_000.times.map do
+      ExIvar.new
+    end
+    EnvUtil.under_gc_compact_stress do
+      10.times do
+        x = ExIvar.new
+        x.instance_variable_set(:@resize, 1)
+        x
+      end
+    end
+  end
+
   def test_local_variables_with_kwarg
     bug11674 = '[ruby-core:71437] [Bug #11674]'
     v = with_kwargs_11(v1:1,v2:2,v3:3,v4:4,v5:5,v6:6,v7:7,v8:8,v9:9,v10:10,v11:11)
diff --git a/variable.c b/variable.c
index 67dc2d3397..b18ec1018a 100644
--- a/variable.c
+++ b/variable.c
@@ -1823,34 +1823,6 @@ struct gen_fields_lookup_ensure_size {
     bool resize;
 };
 
-static int
-generic_fields_lookup_ensure_size(st_data_t *k, st_data_t *v, st_data_t u, int existing)
-{
-    ASSERT_vm_locking();
-
-    struct gen_fields_lookup_ensure_size *fields_lookup = (struct gen_fields_lookup_ensure_size *)u;
-    struct gen_fields_tbl *fields_tbl = existing ? (struct gen_fields_tbl *)*v : NULL;
-
-    if (!existing || fields_lookup->resize) {
-        if (existing) {
-            RUBY_ASSERT(RSHAPE_TYPE_P(fields_lookup->shape_id, SHAPE_IVAR) || RSHAPE_TYPE_P(fields_lookup->shape_id, SHAPE_OBJ_ID));
-            RUBY_ASSERT(RSHAPE_CAPACITY(RSHAPE_PARENT(fields_lookup->shape_id)) < RSHAPE_CAPACITY(fields_lookup->shape_id));
-        }
-
-        fields_tbl = gen_fields_tbl_resize(fields_tbl, RSHAPE_CAPACITY(fields_lookup->shape_id));
-        *v = (st_data_t)fields_tbl;
-    }
-
-    fields_lookup->fields_tbl = fields_tbl;
-    if (fields_lookup->shape_id) {
-        rb_obj_set_shape_id(fields_lookup->obj, fields_lookup->shape_id);
-    }
-
-    RUBY_ASSERT(rb_obj_exivar_p((VALUE)*k));
-
-    return ST_CONTINUE;
-}
-
 static VALUE *
 generic_ivar_set_shape_fields(VALUE obj, void *data)
 {
@@ -1858,8 +1830,27 @@ generic_ivar_set_shape_fields(VALUE obj, void *data)
 
     struct gen_fields_lookup_ensure_size *fields_lookup = data;
 
+    // We can't use st_update, since when resizing the fields table GC can
+    // happen, which will modify the st_table and may rebuild it
     RB_VM_LOCKING() {
-        st_update(generic_fields_tbl(obj, fields_lookup->id, false), (st_data_t)obj, generic_fields_lookup_ensure_size, (st_data_t)fields_lookup);
+        struct gen_fields_tbl *fields_tbl = NULL;
+        st_table *tbl = generic_fields_tbl(obj, fields_lookup->id, false);
+        int existing = st_lookup(tbl, (st_data_t)obj, (st_data_t *)&fields_tbl);
+
+        if (!existing || fields_lookup->resize) {
+            if (existing) {
+                RUBY_ASSERT(RSHAPE_TYPE_P(fields_lookup->shape_id, SHAPE_IVAR) || RSHAPE_TYPE_P(fields_lookup->shape_id, SHAPE_OBJ_ID));
+                RUBY_ASSERT(RSHAPE_CAPACITY(RSHAPE_PARENT(fields_lookup->shape_id)) < RSHAPE_CAPACITY(fields_lookup->shape_id));
+            }
+
+            fields_tbl = gen_fields_tbl_resize(fields_tbl, RSHAPE_CAPACITY(fields_lookup->shape_id));
+            st_insert(tbl, (st_data_t)obj, (st_data_t)fields_tbl);
+        }
+
+        fields_lookup->fields_tbl = fields_tbl;
+        if (fields_lookup->shape_id) {
+            rb_obj_set_shape_id(fields_lookup->obj, fields_lookup->shape_id);
+        }
     }
 
     return fields_lookup->fields_tbl->as.shape.fields;