diff --git a/Makefile b/Makefile
index 584c8ce..8808aac 100644
--- a/Makefile
+++ b/Makefile
@@ -2,6 +2,7 @@ all: bindings
 	python setup.py build
 
 bindings:
+	grep -PhR "(?s)extern [^\"](.*);" WiringPi/ > bindings.i
 	swig2.0 -python wiringpi.i
 
 install: