diff --git a/scripts/mysql_install_db.sh b/scripts/mysql_install_db.sh
index 27256994ef0..fb1663d9d69 100644
--- a/scripts/mysql_install_db.sh
+++ b/scripts/mysql_install_db.sh
@@ -243,6 +243,8 @@ then
 fi
 if test -n "$srcdir"
 then
+  # In an out-of-source build, builddir is not srcdir. Try to guess where
+  # builddir is by looking for my_print_defaults.
   if test -z "$builddir"
   then
     if test -x "$dirname0/extra/my_print_defaults"