diff --git a/riscv64/riscv64spec/spec.go b/riscv64/riscv64spec/spec.go
index b65ea69..5b80c86 100644
--- a/riscv64/riscv64spec/spec.go
+++ b/riscv64/riscv64spec/spec.go
@@ -68,7 +68,7 @@
 	log.SetFlags(0)
 	log.SetPrefix("riscv64spec: ")
 
-	if len(os.Args) < 1 {
+	if len(os.Args) < 2 {
 		log.Fatal("usage: go run spec.go <opcodes-repo-path>")
 	}
 	extensionsPath := filepath.Join(os.Args[1], "extensions")