diff --git a/rust/crates/rusty-claude-cli/src/main.rs b/rust/crates/rusty-claude-cli/src/main.rs
index 738d7c5..b652cf4 100644
--- a/rust/crates/rusty-claude-cli/src/main.rs
+++ b/rust/crates/rusty-claude-cli/src/main.rs
@@ -746,6 +746,31 @@ fn parse_single_word_command_alias(
     permission_mode_override: Option<PermissionMode>,
     output_format: CliOutputFormat,
 ) -> Option<Result<CliAction, String>> {
+    if rest.is_empty() {
+        return None;
+    }
+
+    // Diagnostic verbs (help, version, status, sandbox, doctor, state) accept only the verb itself
+    // or --help / -h as a suffix. Any other suffix args are unrecognized.
+    let verb = &rest[0];
+    let is_diagnostic = matches!(
+        verb.as_str(),
+        "help" | "version" | "status" | "sandbox" | "doctor" | "state"
+    );
+
+    if is_diagnostic && rest.len() > 1 {
+        // Diagnostic verb with trailing args: reject unrecognized suffix
+        if is_help_flag(&rest[1]) && rest.len() == 2 {
+            // "doctor --help" is valid, routed to parse_local_help_action() instead
+            return None;
+        }
+        // Unrecognized suffix like "--json"
+        return Some(Err(format!(
+            "unrecognized argument `{}` for subcommand `{}`",
+            rest[1], verb
+        )));
+    }
+
     if rest.len() != 1 {
         return None;
     }