--- a/src/eval.c
+++ b/src/eval.c
@@ -5725,10 +5725,15 @@ set_ref_in_item_class(
 	return FALSE;
 
     cl->class_copyID = copyID;
-    for (int i = 0; !abort && i < cl->class_class_member_count; ++i)
-	abort = abort || set_ref_in_item(
-		&cl->class_members_tv[i],
-		copyID, ht_stack, list_stack);
+    if (cl->class_members_tv != NULL)
+    {
+	// The "class_members_tv" table is allocated only for regular classes
+	// and not for interfaces.
+	for (int i = 0; !abort && i < cl->class_class_member_count; ++i)
+	    abort = abort || set_ref_in_item(
+		    &cl->class_members_tv[i],
+		    copyID, ht_stack, list_stack);
+    }
 
     for (int i = 0; !abort && i < cl->class_class_function_count; ++i)
 	abort = abort || set_ref_in_func(NULL,

--- a/src/testdir/test_vim9_class.vim
+++ b/src/testdir/test_vim9_class.vim
@@ -1307,6 +1307,60 @@ func Test_class_garbagecollect()
   call v9.CheckScriptSuccess(lines)
 endfunc
 
+" Test interface garbage collection
+func Test_interface_garbagecollect()
+  let lines =<< trim END
+    vim9script
+
+    interface I
+      static ro_class_var: number
+      public static rw_class_var: number
+      static _priv_class_var: number
+      this.ro_obj_var: number
+      public this.rw_obj_var: number
+      this._priv_obj_var: number
+
+      static def ClassFoo(): number
+      static def _ClassBar(): number
+      def ObjFoo(): number
+      def _ObjBar(): number
+    endinterface
+
+    class A implements I
+      static ro_class_var: number = 10
+      public static rw_class_var: number = 20
+      static _priv_class_var: number = 30
+      this.ro_obj_var: number = 40
+      public this.rw_obj_var: number = 50
+      this._priv_obj_var: number = 60
+
+      static def _ClassBar(): number
+        return _priv_class_var
+      enddef
+
+      static def ClassFoo(): number
+        return ro_class_var + rw_class_var + A._ClassBar()
+      enddef
+
+      def _ObjBar(): number
+        return this._priv_obj_var
+      enddef
+
+      def ObjFoo(): number
+        return this.ro_obj_var + this.rw_obj_var + this._ObjBar()
+      enddef
+    endclass
+
+    assert_equal(60, A.ClassFoo())
+    var o = A.new()
+    assert_equal(150, o.ObjFoo())
+    test_garbagecollect_now()
+    assert_equal(60, A.ClassFoo())
+    assert_equal(150, o.ObjFoo())
+  END
+  call v9.CheckScriptSuccess(lines)
+endfunc
+
 def Test_class_function()
   var lines =<< trim END
       vim9script

--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@ static char *(features[]) =
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1865,
+/**/
     1864,
 /**/
     1863,