diff --git a/parse.y b/parse.y
index 028b89c070..ee48ad4f79 100644
--- a/parse.y
+++ b/parse.y
@@ -6392,6 +6392,11 @@ dedent_string(VALUE string, int width)
 	    break;
 	}
     }
+    if (!i) return 0;
+    rb_str_modify(string);
+    str = RSTRING_PTR(string);
+    if (RSTRING_LEN(string) != len)
+	rb_fatal("literal string changed: %+"PRIsVALUE, string);
     MEMMOVE(str, str + i, char, len - i);
     rb_str_set_len(string, len - i);
     return i;
@@ -6448,7 +6453,6 @@ parser_dedent_string(VALUE self, VALUE input, VALUE width)
 
     StringValue(input);
     wid = NUM2UINT(width);
-    rb_str_modify(input);
     col = dedent_string(input, wid);
     return INT2NUM(col);
 }
diff --git a/test/ruby/test_parse.rb b/test/ruby/test_parse.rb
index 56e1020c5a..6030dad605 100644
--- a/test/ruby/test_parse.rb
+++ b/test/ruby/test_parse.rb
@@ -988,6 +988,16 @@ x = __ENCODING__
     assert_equal(-100, e.backtrace_locations.first.lineno, bug)
   end
 
+  def test_file_in_indented_heredoc
+    name = '[ruby-core:80987] [Bug #13540]' # long enough to be shared
+    assert_equal(name+"\n", eval("#{<<-"begin;"}\n#{<<-'end;'}", nil, name))
+    begin;
+      <<~HEREDOC
+        #{__FILE__}
+      HEREDOC
+    end;
+  end
+
 =begin
   def test_past_scope_variable
     assert_warning(/past scope/) {catch {|tag| eval("BEGIN{throw tag}; tap {a = 1}; a")}}