Index: mono/metadata/w32process-unix-bsd.c
--- mono/metadata/w32process-unix-bsd.c.orig
+++ mono/metadata/w32process-unix-bsd.c
@@ -7,6 +7,7 @@
 
 #ifdef USE_BSD_BACKEND
 
+#include <signal.h>
 #include <errno.h>
 #include <signal.h>
 #include <sys/proc.h>