diff --git a/src/maths/KLU/klu_utils.c b/src/maths/KLU/klu_utils.c
index becb7c446..db23f5ea6 100644
--- a/src/maths/KLU/klu_utils.c
+++ b/src/maths/KLU/klu_utils.c
@@ -1,3 +1,4 @@
+#include <stdio.h>
 #include "ngspice/memory.h"
 #include "klu_internal.h"