diff --git a/modules/DESCR b/modules/DESCR
new file mode 100644
index 0000000..5d47163
--- /dev/null
+++ b/modules/DESCR
@@ -0,0 +1,7 @@
+USB-A-PCB: Figure 6-9 (page 99) of the
+  Universal Serial Bus Specification;
+  Revision 2.0; April 27, 2000
+USB-A-PCB: http://www.poweredusb.org/pdf/usb20.pdf
+# unofficial copy of the specification. We reference it here because the
+# original is in a ZIP, making access less convenient:
+# http://www.usb.org/developers/docs/usb_20_071012.zip
diff --git a/modules/Makefile b/modules/Makefile
index a07d38a..f08bc0a 100644
--- a/modules/Makefile
+++ b/modules/Makefile
@@ -32,7 +32,8 @@ spotless:	clean
 		fped -k $< $@
 
 catalog catalog.pdf: HIERARCHY $(MODULES:%=%.fpd)
-		gencat -F -p $(MODULES:%=-l %.fpd) HIERARCHY >catalog.pdf || \
+		gencat -F -p $(MODULES:%=-l %.fpd) HIERARCHY DESCR \
+		  >catalog.pdf || \
 		  { rm -f catalog.pdf; exit 1; }
 
 view:		catalog.pdf