diff --git a/src/config_libconfig.c b/src/config_libconfig.c
index e8eeb4b..e9818eb 100644
--- a/src/config_libconfig.c
+++ b/src/config_libconfig.c
@@ -448,11 +448,11 @@ char *parse_config_libconfig(options_t *opt, const char *config_file, bool *shad
 	}
 	// --vsync
 	if (config_lookup_string(&cfg, "vsync", &sval)) {
-		opt->vsync = parse_vsync(sval);
-		log_warn("vsync option will take a boolean from now on. \"%s\" is "
-		         "interpreted as \"%s\" for compatibility, but this will stop "
-		         "working soon",
-		         sval, opt->vsync ? "true" : "false");
+		bool parsed_vsync = parse_vsync(sval);
+		log_error("vsync option will take a boolean from now on. \"%s\" in "
+		          "your configuration should be changed to \"%s\"",
+		          sval, parsed_vsync ? "true" : "false");
+		goto err;
 	}
 	lcfg_lookup_bool(&cfg, "vsync", &opt->vsync);
 	// --backend
diff --git a/src/options.c b/src/options.c
index 278405d..e0a1713 100644
--- a/src/options.c
+++ b/src/options.c
@@ -636,11 +636,11 @@ bool get_cfg(options_t *opt, int argc, char *const *argv, bool shadow_enable,
 			break;
 		case 270:
 			if (optarg) {
-				opt->vsync = parse_vsync(optarg);
-				log_warn("--vsync doesn't take argument anymore. \"%s\" "
-					 "is interpreted as \"%s\" for compatibility, but "
-					 "this will stop working soon",
-					 optarg, opt->vsync ? "true" : "false");
+				bool parsed_vsync = parse_vsync(optarg);
+				log_error("--vsync doesn't take argument anymore. \"%s\" "
+				          "should be changed to \"%s\"",
+				          optarg, parsed_vsync ? "true" : "false");
+				failed = true;
 			} else {
 				opt->vsync = true;
 			}