diff --git a/doc/doxygen/generate.sh b/doc/doxygen/generate.sh
index 99afb124..89344b0e 100755
--- a/doc/doxygen/generate.sh
+++ b/doc/doxygen/generate.sh
@@ -1 +1,3 @@
+#!/bin/sh
+
 doxygen lwip.Doxyfile