diff --git a/ast.c b/ast.c
index 202527f53f..e1c044e24c 100644
--- a/ast.c
+++ b/ast.c
@@ -213,6 +213,9 @@ ast_s_of(rb_execution_context_t *ec, VALUE module, VALUE body, VALUE keep_script
         else {
             iseq = rb_method_iseq(body);
         }
+        if (!iseq) {
+            rb_raise(rb_eArgError, "cannot get AST for method that is not defined in Ruby");
+        }
         if (rb_iseq_from_eval_p(iseq)) {
             rb_raise(rb_eArgError, "cannot get AST for method defined in eval");
         }
diff --git a/test/ruby/test_ast.rb b/test/ruby/test_ast.rb
index 3af67b1495..0b5c41058c 100644
--- a/test/ruby/test_ast.rb
+++ b/test/ruby/test_ast.rb
@@ -231,6 +231,11 @@ class TestAst < Test::Unit::TestCase
     assert_raise(ArgumentError) { RubyVM::AbstractSyntaxTree.of(method) }
   end
 
+  def test_of_c_method
+    c = Class.new { attr_reader :foo }
+    assert_raise(ArgumentError) { RubyVM::AbstractSyntaxTree.of(c.instance_method(:foo)) }
+  end
+
   def test_scope_local_variables
     node = RubyVM::AbstractSyntaxTree.parse("_x = 0")
     lv, _, body = *node.children