diff --git a/hermit/tools/proxy.c b/hermit/tools/proxy.c
index 36de2ca95..c922aed45 100644
--- a/hermit/tools/proxy.c
+++ b/hermit/tools/proxy.c
@@ -397,6 +397,7 @@ int handle_syscalls(int s)
 		}
 		default:
 			fprintf(stderr, "Proxy: invalid syscall number %d\n", sysnr);
+			exit(1);
 			break;
 		}
 	}