diff --git a/include/ruby/intern.h b/include/ruby/intern.h
index 56e2452..d9541ca 100644
--- a/include/ruby/intern.h
+++ b/include/ruby/intern.h
@@ -583,6 +583,7 @@ void rb_backref_set(VALUE);
 VALUE rb_lastline_get(void);
 void rb_lastline_set(VALUE);
 VALUE rb_sym_all_symbols(void);
+VALUE rb_sym_lookup(int argc, VALUE *argv);
 /* process.c */
 void rb_last_status_set(int status, rb_pid_t pid);
 VALUE rb_last_status_get(void);
diff --git a/parse.y b/parse.y
index 915db67..3931351 100644
--- a/parse.y
+++ b/parse.y
@@ -10413,6 +10413,38 @@ rb_sym_all_symbols(void)
     return ary;
 }
 
+/*
+ *  call-seq:
+ *     Symbol[str]    => Symbol or nil
+ *
+ *  Returns an extant symbol, which is the .to_sym of +str+, or
+ *  nil if no such symbol exists.
+ *
+ *     Symbol['Object']      #=> :Object
+ *     Symbol['none such']   #=> nil
+ */
+
+VALUE
+rb_sym_lookup(int argc, VALUE *argv)
+{
+    st_data_t id;
+    VALUE str,tmp;
+    rb_scan_args(argc, argv, "1", &str);
+    if (!RB_TYPE_P(str, T_STRING)) {
+	tmp = rb_check_string_type(str);
+	if (NIL_P(tmp)) {
+	    tmp = rb_inspect(str);
+	    rb_raise(rb_eTypeError, "%s is not a string",
+		     RSTRING_PTR(tmp));
+	}
+        str = tmp;
+    }
+    if (st_lookup(global_symbols.sym_id, (st_data_t)str, &id)) {
+	return ID2SYM(id);
+    }
+    return Qnil;
+}
+
 int
 rb_is_const_id(ID id)
 {
diff --git a/string.c b/string.c
index 04984f0..3bae1b7 100644
--- a/string.c
+++ b/string.c
@@ -8307,6 +8307,7 @@ Init_String(void)
     rb_undef_alloc_func(rb_cSymbol);
     rb_undef_method(CLASS_OF(rb_cSymbol), "new");
     rb_define_singleton_method(rb_cSymbol, "all_symbols", rb_sym_all_symbols, 0); /* in parse.y */
+    rb_define_singleton_method(rb_cSymbol, "[]", rb_sym_lookup, -1); /* in parse.y */
 
     rb_define_method(rb_cSymbol, "==", sym_equal, 1);
     rb_define_method(rb_cSymbol, "===", sym_equal, 1);