diff --git a/src/spicelib/analysis/optran.c b/src/spicelib/analysis/optran.c
index 7986fecb9..60d30acdf 100644
--- a/src/spicelib/analysis/optran.c
+++ b/src/spicelib/analysis/optran.c
@@ -6,6 +6,8 @@ Modified BSD license
 
 /* subroutine to generate OP by TRANSIENT analysis */
 
+#include <errno.h>
+
 #include "ngspice/ngspice.h"
 #include "ngspice/cktdefs.h"
 #include "cktaccept.h"