diff --git a/doc/Doxyfile.in b/doc/Doxyfile.in
--- a/doc/Doxyfile.in
+++ b/doc/Doxyfile.in
@@ -89,6 +89,7 @@
                          "@abs_top_srcdir@/lemon/bits" \
                          "@abs_top_srcdir@/lemon/concepts" \
                          "@abs_top_srcdir@/demo" \
+                         "@abs_top_srcdir@/contrib" \
                          "@abs_top_srcdir@/tools" \
                          "@abs_top_srcdir@/test/test_tools.h" \
                          "@abs_top_builddir@/doc/references.dox"