diff --git a/explorer/gen_rtti.py b/explorer/gen_rtti.py
index 4356df74ff68..374c6870d86f 100755
--- a/explorer/gen_rtti.py
+++ b/explorer/gen_rtti.py
@@ -2,6 +2,8 @@
 
 """Generates C++ header to support LLVM-style RTTI for a class hierarchy.
 
+This script should be run through the //explorer:gen_rtti build target.
+
 # Background
 
 A C++ class hierarchy supported by this script consists of *abstract* classes,