diff --git a/glu.pc.in b/glu.pc.in
index 939740d..8bb957a 100644
--- a/glu.pc.in
+++ b/glu.pc.in
@@ -9,3 +9,4 @@ Requires: @GLU_REQUIRES@
 Version: @VERSION@
 Libs: -L${libdir} -lGLU
 Libs.private: -lm
+Cflags: -I${includedir}
diff --git a/src/libutil/error.c b/src/libutil/error.c
index 7212748..d3b2666 100644
--- a/src/libutil/error.c
+++ b/src/libutil/error.c
@@ -30,6 +30,7 @@

 #include "gluos.h"
 #include "gluint.h"
+#include <stddef.h>
 #include <GL/glu.h>