diff --git a/gc.c b/gc.c
index 262dfe7d04..4bccc30037 100644
--- a/gc.c
+++ b/gc.c
@@ -2343,7 +2343,7 @@ id2ref(VALUE obj, VALUE objid)
  *  Note that some objects of builtin classes are reused for optimization.
  *  This is the case for immediate values and frozen string litterals.
  *  Immediate values are not passed by reference by are passed by value:
- *  +nil+, +true+, +false+, Fixnums. Some Floats may be immediates too.
+ *  +nil+, +true+, +false+, Fixnums, Symbols. Some Floats may be immediates too.
  *
  *      Object.new.object_id  == Object.new.object_id  # => false
  *      (21 * 2).object_id    == (21 * 2).object_id    # => true