diff --git a/doc/manual/Makefile b/doc/manual/Makefile
index ee92364f9..aded43e3f 100644
--- a/doc/manual/Makefile
+++ b/doc/manual/Makefile
@@ -63,7 +63,8 @@ SOURCES = \
 # documentation formats (html, latex...) the following formats are supported:
 #  1) a single .dia file (preferred option, because it can be edited)
 #  2) a single .eps file
-#  3) both a .pdf and .png file
+#  3) a single .png file
+#  4) both a .pdf and .png file
 
 SOURCEFIGS = \
     figures/software-organization.dia \
diff --git a/doc/models/Makefile b/doc/models/Makefile
index 5ec32ed76..ee36715e4 100644
--- a/doc/models/Makefile
+++ b/doc/models/Makefile
@@ -101,7 +101,8 @@ SOURCES = \
 # documentation formats (html, latex...) the following formats are supported:
 #  1) a single .dia file (preferred option, because it can be edited)
 #  2) a single .eps file
-#  3) both a .pdf and .png file
+#  3) a single .png file
+#  4) both a .pdf and .png file
 SOURCEFIGS = \
 	figures/testbed.dia \
 	figures/emulated-channel.dia \