diff --git a/src/maths/KLU/btf_strongcomp.c b/src/maths/KLU/btf_strongcomp.c
index 3ecd0ad87..5de9a98fd 100644
--- a/src/maths/KLU/btf_strongcomp.c
+++ b/src/maths/KLU/btf_strongcomp.c
@@ -11,6 +11,7 @@
  */
 
 #include "ngspice/btf.h"
+#include "ngspice/defines.h"
 #include "btf_internal.h"
 
 #define UNVISITED (-2)      /* Flag [j] = UNVISITED if node j not visited yet */
diff --git a/src/maths/KLU/klu_internal.h b/src/maths/KLU/klu_internal.h
index 15576e687..910f9c331 100644
--- a/src/maths/KLU/klu_internal.h
+++ b/src/maths/KLU/klu_internal.h
@@ -10,6 +10,7 @@
 #include "ngspice/klu.h"
 #include "ngspice/btf.h"
 #include "klu_version.h"
+#include "klu_proto.h"
 
 /* ========================================================================== */
 /* make sure debugging and printing is turned off */