Index: usr.sbin/bhyve/bhyverun.c
===================================================================
--- usr.sbin/bhyve/bhyverun.c
+++ usr.sbin/bhyve/bhyverun.c
@@ -69,6 +69,7 @@
 #include <sysexits.h>
 #include <stdbool.h>
 #include <stdint.h>
+#include <uuid.h>
 #ifdef BHYVE_SNAPSHOT
 #include <ucl.h>
 #include <unistd.h>
@@ -1077,6 +1078,16 @@
 	fbsdrun_addcpu(ctx, BSP, vcpu, rip);
 }
 
+bool 
+is_valid_uuid(const char* uuid_str)
+{
+	uuid_t uuid;
+	uint32_t uuid_status;
+
+	uuid_from_string(uuid_str, &uuid, &uuid_status);
+	return  uuid_status == uuid_s_ok;
+}
+
 int
 main(int argc, char *argv[])
 {
@@ -1196,7 +1207,10 @@
 			rtc_localtime = 0;
 			break;
 		case 'U':
-			guest_uuid_str = optarg;
+			if (is_valid_uuid(optarg) == false) {
+				errx(EX_USAGE, "invalid UUID '%s'", optarg);
+			}
+			guest_uuid_str = optarg;	
 			break;
 		case 'w':
 			strictmsr = 0;