diff --git a/INSTALL b/INSTALL
index 86f9e0080c..595f711ffc 100644
--- a/INSTALL
+++ b/INSTALL
@@ -214,6 +214,24 @@ like 'apt-get build-dep emacs' (on older systems, replace 'emacs' with
 eg 'emacs25').  On Red Hat-based systems, the corresponding command is
 'dnf builddep emacs' (on older systems, use 'yum-builddep' instead).

+* GNU/Linux source packages
+
+Many GNU/Linux systems provide separate packages containing the
+sources of Emacs.  They are useful if you want to check the source
+code of Emacs primitive functions, and alike.
+
+The names of the packages that you need varies according to the
+GNU/Linux distribution that you use.  On Debian-based systems, you can
+install all the packages needed to build the installed version of
+Emacs with a command like 'apt-get source' (on older systems, replace
+'emacs' with eg 'emacs25').  On Red Hat-based systems, the
+corresponding command is <tbd>.
+
+Once you have installed the source package, for example at
+/path/to/emacs-26.1+1, add the following line to your startup file:
+
+     (setq source-directory "/path/to/emacs-26.1+1")
+

 DETAILED BUILDING AND INSTALLATION: