diff --git a/include/QF/sys.h b/include/QF/sys.h
index 47bc6c401..1b2d3e070 100644
--- a/include/QF/sys.h
+++ b/include/QF/sys.h
@@ -78,7 +78,7 @@ void Sys_RegisterShutdown (void (*func) (void));
 double Sys_DoubleTime (void);
 void Sys_TimeOfDay(date_t *date);
 
-int Sys_CheckInput (int idle, unsigned int net_socket);
+int Sys_CheckInput (int idle, int net_socket);
 const char *Sys_ConsoleInput (void);
 
 void Sys_Sleep (void);
diff --git a/libs/util/sys.c b/libs/util/sys.c
index cfde73755..1be18de4e 100644
--- a/libs/util/sys.c
+++ b/libs/util/sys.c
@@ -504,7 +504,7 @@ Sys_DebugLog (const char *file, const char *fmt, ...)
 }
 
 int
-Sys_CheckInput (int idle, unsigned int net_socket)
+Sys_CheckInput (int idle, int net_socket)
 {
 	fd_set      fdset;
 	int         res;
@@ -538,7 +538,7 @@ Sys_CheckInput (int idle, unsigned int net_socket)
 		FD_SET (0, &fdset);
 #endif
 	if (net_socket >= 0)
-		FD_SET (net_socket, &fdset);
+		FD_SET (((unsigned) net_socket), &fdset);	// cast needed for windows
 
 	if (!idle || !sys_dead_sleep->int_val)
 		timeout = &_timeout;