diff --git a/Makefile b/Makefile
index 068ad6dcdd..ae043f2822 100644
--- a/Makefile
+++ b/Makefile
@@ -495,7 +495,7 @@ else
 	@echo "<docs xmlns:xi=\"http://www.w3.org/2001/XInclude\">" >> $@
 	@for x in $(MOD_SUBDIRS); do \
 		printf "$$x " ; \
-		for i in $$x/*.c; do \
+		for i in `find $$x -name '*.c'`; do \
 			$(PYTHON) build_tools/get_documentation.py < $$i >> $@ ; \
 		done ; \
 	done