diff --git a/ext/-test-/funcall/passing_block.c b/ext/-test-/funcall/funcall.c
similarity index 56%
rename from ext/-test-/funcall/passing_block.c
rename to ext/-test-/funcall/funcall.c
index 70cb210831..4e13c952e5 100644
--- a/ext/-test-/funcall/passing_block.c
+++ b/ext/-test-/funcall/funcall.c
@@ -14,10 +14,21 @@ with_funcall_passing_block(int argc, VALUE *argv, VALUE self)
     return rb_funcall_passing_block(self, rb_intern("target"), argc, argv);
 }
 
+static VALUE
+extra_args_name(VALUE self)
+{
+    /*
+     * at least clang 5.x gets tripped by the extra 0 arg
+     * [ruby-core:85266] [Bug #14425]
+     */
+    return rb_funcall(self, rb_intern("name"), 0, 0);
+}
+
 void
 Init_funcall(void)
 {
-    VALUE cRelay = rb_path2class("TestFuncall::Relay");
+    VALUE cTestFuncall = rb_path2class("TestFuncall");
+    VALUE cRelay = rb_define_module_under(cTestFuncall, "Relay");
 
     rb_define_singleton_method(cRelay,
 			       "with_funcall2",
@@ -27,4 +38,7 @@ Init_funcall(void)
 			       "with_funcall_passing_block",
 			       with_funcall_passing_block,
 			       -1);
+    rb_define_singleton_method(cTestFuncall, "extra_args_name",
+                                extra_args_name,
+                                0);
 }
diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index bd635f3b7c..372b16891b 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -1783,6 +1783,8 @@ VALUE rb_check_symbol(volatile VALUE *namep);
 # if defined(HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P)
 #   if HAVE_ATTRIBUTE_ERRORFUNC
 ERRORFUNC((" argument length doesn't match"), int rb_varargs_bad_length(int,int));
+#   elif defined(__clang__) /* [ruby-core:85266] [Bug #14425] */
+#     define rb_varargs_bad_length(argc, vargc) ((argc)/((argc) <= (vargc)))
 #   else
 #     define rb_varargs_bad_length(argc, vargc) ((argc)/((argc) == (vargc)))
 #   endif
diff --git a/test/-ext-/funcall/test_funcall.rb b/test/-ext-/funcall/test_funcall.rb
new file mode 100644
index 0000000000..01a03bf5ef
--- /dev/null
+++ b/test/-ext-/funcall/test_funcall.rb
@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+require 'test/unit'
+
+class TestFuncall < Test::Unit::TestCase
+  require '-test-/funcall'
+
+  def test_funcall_extra_args
+    assert_equal 'TestFuncall', TestFuncall.extra_args_name,
+	 '[ruby-core:85266] [Bug #14425]'
+  end
+end