--- fet-5.26.1.old/src/interface/fet.cpp
+++ fet-5.26.1/src/interface/fet.cpp
@@ -19,6 +19,10 @@
  *                                                                         *
  ***************************************************************************/
 
+extern "C" {
+#include <stdlib.h>
+}
+
 #include "fet.h"
 
 #include "matrix.h"