diff --git a/Src/main.c b/Src/main.c
index 8897ffd..f441520 100644
--- a/Src/main.c
+++ b/Src/main.c
@@ -753,54 +753,52 @@ optimizations(int nr)
 	case '1':
 		dataflow = 1 - dataflow; /* dataflow */
 		if (verbose&32)
-		printf("spin: dataflow optimizations turned %s\n",
-			dataflow?"on":"off");
-		break;
-	case '2':
+      printf("spin: dataflow optimizations turned %s\n",
+        dataflow?"on":"off");
+    break;
+    case '2':
 		/* dead variable elimination */
 		deadvar = 1 - deadvar;
 		if (verbose&32)
-		printf("spin: dead variable elimination turned %s\n",
-			deadvar?"on":"off");
-		break;
+      printf("spin: dead variable elimination turned %s\n",
+        deadvar?"on":"off");
+    break;
 	case '3':
 		/* statement merging */
 		merger = 1 - merger;
 		if (verbose&32)
 		printf("spin: statement merging turned %s\n",
 			merger?"on":"off");
-		break;
-
+    break;
 	case '4':
 		/* rv optimization */
 		rvopt = 1 - rvopt;
 		if (verbose&32)
 		printf("spin: rendezvous optimization turned %s\n",
 			rvopt?"on":"off");
-		break;
+    break;
 	case '5':
 		/* case caching */
 		ccache = 1 - ccache;
 		if (verbose&32)
-		printf("spin: case caching turned %s\n",
-			ccache?"on":"off");
-		break;
+      printf("spin: case caching turned %s\n",
+        ccache?"on":"off");
+    break;
 	case '6':
 		old_priority_rules = 1;
 		if (verbose&32)
-		printf("spin: using old priority rules (pre version 6.2)\n");
-		return 0; /* no break */
+      printf("spin: using old priority rules (pre version 6.2)\n");
+    return 0; /* no break */
 	case '7':
 		implied_semis = 0;
 		if (verbose&32)
-		printf("spin: no implied semi-colons (pre version 6.3)\n");
-		return 0; /* no break */
+      printf("spin: no implied semi-colons (pre version 6.3)\n");
+    return 0; /* no break */
 	default:
-		printf("spin: bad or missing parameter on -o\n");
-		// usage();
-		break;
+    return -1; // TODO: Improve the failure mode for argument parsing
 	}
-	return 1;
+
+	return 0;
 }
 
 static void
@@ -1004,7 +1002,14 @@ static error_t parse_opt(int key, char *arg, struct argp_state *state) {
     }
     case 'n': args->T = atoi(arg); tl_terse = 1; break;
     case 'O': old_scope_rules = 1; break;
-    case 'o': args->usedopts += optimizations(atoi(arg)); break;
+    case 'o': {
+      args->usedopts += optimizations(arg[0]);
+      if (args->usedopts == -1) {
+        argp_failure(state, 0, 1, "bad or missing parameter on -o: %d", atoi(arg));
+        return EINVAL;
+      }
+      break;
+    }
     case 'P': {
       assert(strlen(arg) < sizeof(PreProc));
       strcpy(PreProc, arg);