diff --git a/src/platform/commandline.c b/src/platform/commandline.c
index eecf19250..e79543444 100644
--- a/src/platform/commandline.c
+++ b/src/platform/commandline.c
@@ -15,6 +15,7 @@ static const char* _defaultFilename = "test.rom";
 
 static const struct option _options[] = {
 	{ "bios", 1, 0, 'b' },
+	{ "debug", 1, 0, 'd' },
 	{ "gdb", 1, 0, 'g' },
 	{ 0, 0, 0, 0 }
 };
@@ -27,14 +28,18 @@ int parseCommandArgs(struct StartupOptions* opts, int argc, char* const* argv) {
 	opts->height = 160;
 	opts->fullscreen = 0;
 
+	int multiplier = 1;
 	int ch;
-	while ((ch = getopt_long(argc, argv, "b:dfg", _options, 0)) != -1) {
+	while ((ch = getopt_long(argc, argv, "234b:dfg", _options, 0)) != -1) {
 		switch (ch) {
 		case 'b':
 			opts->biosFd = open(optarg, O_RDONLY);
 			break;
 #ifdef USE_CLI_DEBUGGER
 		case 'd':
+			if (opts->debuggerType != DEBUGGER_NONE) {
+				return 0;
+			}
 			opts->debuggerType = DEBUGGER_CLI;
 			break;
 #endif
@@ -43,19 +48,37 @@ int parseCommandArgs(struct StartupOptions* opts, int argc, char* const* argv) {
 			break;
 #ifdef USE_GDB_STUB
 		case 'g':
+			if (opts->debuggerType != DEBUGGER_NONE) {
+				return 0;
+			}
 			opts->debuggerType = DEBUGGER_GDB;
 			break;
 #endif
+		case '2':
+			multiplier = 2;
+			break;
+		case '3':
+			multiplier = 3;
+			break;
+		case '4':
+			multiplier = 4;
+			break;
+		default:
+			return 0;
 		}
 	}
 	argc -= optind;
 	argv += optind;
-	if (argc) {
+	if (argc == 1) {
 		opts->fname = argv[0];
-	} else {
+	} else if (argc == 0) {
 		opts->fname = _defaultFilename;
+	} else {
+		return 0;
 	}
 	opts->fd = open(opts->fname, O_RDONLY);
+	opts->width *= multiplier;
+	opts->height *= multiplier;
 	return 1;
 }
 
@@ -81,6 +104,7 @@ struct ARMDebugger* createDebugger(struct StartupOptions* opts) {
 #ifdef USE_GDB_STUB
 	case DEBUGGER_GDB:
 		GDBStubCreate(&debugger->gdb);
+		GDBStubListen(&debugger->gdb, 2345, 0);
 		break;
 #endif
 	case DEBUGGER_NONE:
@@ -94,5 +118,17 @@ struct ARMDebugger* createDebugger(struct StartupOptions* opts) {
 }
 
 void usage(const char* arg0) {
-	printf("%s: bad arguments\n", arg0);
+	printf("usage: %s [option ...] file\n", arg0);
+	printf("\nOptions:\n");
+	printf("  -2               2x viewport\n");
+	printf("  -3               3x viewport\n");
+	printf("  -4               4x viewport\n");
+	printf("  -b, --bios FILE  GBA BIOS file to use\n");
+#ifdef USE_CLI_DEBUGGER
+	printf("  -d, --debug      Use command-line debugger\n");
+#endif
+	printf("  -f               Sart full-screen\n");
+#ifdef USE_GDB_STUB
+	printf("  -g, --gdb        Start GDB session (default port 2345)\n");
+#endif
 }