diff --git a/doc/hooks/cernlib.section.md b/doc/hooks/cernlib.section.md
new file mode 100644
index 000000000000..e12b49e127ea
--- /dev/null
+++ b/doc/hooks/cernlib.section.md
@@ -0,0 +1,3 @@
+# CERNLIB {#cernlib-hook}
+
+This hook sets the `CERN`, `CERN_LEVEL`, and `CERN_ROOT` environment variables. They are part of [CERNLIB's build system](https://cernlib.web.cern.ch/install/install.html), and are are needed for some programs to compile correctly.
diff --git a/doc/hooks/index.md b/doc/hooks/index.md
index 6d01c6cbcbe5..42a6553344b2 100644
--- a/doc/hooks/index.md
+++ b/doc/hooks/index.md
@@ -10,6 +10,7 @@ automake.section.md
 autopatchelf.section.md
 bmake.section.md
 breakpoint.section.md
+cernlib.section.md
 cmake.section.md
 gdk-pixbuf.section.md
 ghc.section.md