diff --git a/src/compiler/crystal/macros.cr b/src/compiler/crystal/macros.cr
index 4786b0825f91..5ccc9310fdb4 100644
--- a/src/compiler/crystal/macros.cr
+++ b/src/compiler/crystal/macros.cr
@@ -1752,6 +1752,7 @@ module Crystal::Macros
     end
 
     # Returns the instance variables of this type.
+    # Can only be called from within methods (not top-level code), otherwise will return an empty list.
     def instance_vars : ArrayLiteral(MetaVar)
     end