diff --git a/src/client/client_cli.c b/src/client/client_cli.c
index 4a3ca80..c1e656c 100644
--- a/src/client/client_cli.c
+++ b/src/client/client_cli.c
@@ -814,6 +814,13 @@ int parse_args(Config* config, int argc, char* argv[], int* positional_args,
     } else if (opt_is(argv[i], "--compress-threads", NULL) && i + 1 < argc) {
       if (set_compression_threads_option(&config->compression_threads, argv[++i]) != 0)
         return -1;
+    } else if (opt_is(argv[i], "--checksum-choice", "--cc")) {
+      if (i + 1 >= argc) {
+        log_message(LOG_LEVEL_ERROR, "missing argument for %s", argv[i]);
+        return -1;
+      }
+      log_message(LOG_LEVEL_ERROR, "%s is not supported yet (xxHash64 is used)", argv[i]);
+      return -1;
     } else if (argv[i][0] == '-') {
       char* escaped = output_escape(argv[i], false);
       fprintf(stderr, "Unknown option: %s\n", escaped ? escaped : "<allocation failed>");
diff --git a/src/client/usage.c b/src/client/usage.c
index 94c9d4e..7aa0b3d 100644
--- a/src/client/usage.c
+++ b/src/client/usage.c
@@ -38,6 +38,8 @@ void print_usage(void) {
   printf("  -@, --modify-window <sec>  Modification time tolerance\n");
   printf("  -u, --update        Skip files newer than the source on receiver\n");
   printf("  --existing          Skip files not already present at destination\n");
+  printf("  --checksum-choice, --cc <alg>  Checksum algorithm (not supported yet; xxHash64 is "
+         "used)\n");
   printf("  --delta             Delta transfer for changed files (requires --incremental)\n");
   printf("  -W, --whole-file    Transfer changed files without delta processing\n");
   printf("  --delta-block <n>   Delta block size in bytes (default: %d)\n",
diff --git a/tests/test_client_cli.c b/tests/test_client_cli.c
index 435ffcc..e9d73ca 100644
--- a/tests/test_client_cli.c
+++ b/tests/test_client_cli.c
@@ -753,6 +753,21 @@ static void test_parse_args_no_preserve_blocks_implicit_metadata() {
   }
 }
 
+/* Checksum-choice spellings are recognized and rejected until algorithms are implemented. */
+static void test_parse_args_checksum_choice_aliases() {
+  static const char* const options[] = {"--checksum-choice", "--cc"};
+
+  for (size_t i = 0; i < sizeof(options) / sizeof(options[0]); i++) {
+    Config* cfg = config_create();
+    char* argv[] = {"fastsync", (char*)options[i], "xxh64", "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+
+    EXPECT_EQ_INT(parse_args(cfg, 5, argv, positional_args, &positional_count), -1);
+    config_delete(cfg);
+  }
+}
+
 static void test_parse_args_rejects_unsafe_negation() {
   static const char* const options[] = {"--no-archive", "--no-timeout", "--no-unknown"};
   for (size_t i = 0; i < sizeof(options) / sizeof(options[0]); i++) {
@@ -766,6 +781,21 @@ static void test_parse_args_rejects_unsafe_negation() {
   }
 }
 
+/* Both checksum-choice spellings require a value. */
+static void test_parse_args_checksum_choice_requires_value() {
+  static const char* const options[] = {"--checksum-choice", "--cc"};
+
+  for (size_t i = 0; i < sizeof(options) / sizeof(options[0]); i++) {
+    Config* cfg = config_create();
+    char* argv[] = {"fastsync", (char*)options[i]};
+    int positional_args[2];
+    int positional_count = 0;
+
+    EXPECT_EQ_INT(parse_args(cfg, 2, argv, positional_args, &positional_count), -1);
+    config_delete(cfg);
+  }
+}
+
 static void test_parse_args_old_args() {
   Config* cfg = config_create();
   char* argv[] = {"fastsync", "--old-args", "/src", "/dst"};
@@ -1059,7 +1089,7 @@ void test_client_cli() {
   test_parse_args_info_verbose_order();
   test_parse_args_rejects_invalid_info_flag();
   test_parse_args_archive();
-test_parse_args_negations();
+  test_parse_args_negations();
   test_parse_args_negation_order();
   test_parse_args_no_preserve_blocks_implicit_metadata();
   test_parse_args_rejects_unsafe_negation();
@@ -1080,4 +1110,6 @@ test_parse_args_negations();
   test_parse_args_rejects_invalid_compression_level_equals();
   test_parse_args_rejects_invalid_compression_choice();
   test_parse_args_partial_progress();
+  test_parse_args_checksum_choice_aliases();
+  test_parse_args_checksum_choice_requires_value();
 }