#include "cache.h"
+#include "config.h"
 #include "diff.h"
 #include "commit.h"
 #include "revision.h"
        int i;
        int result;
 
+       if (argc == 2 && !strcmp(argv[1], "-h"))
+               usage(diff_cache_usage);
+
        git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
        init_revisions(&rev, prefix);
        gitmodules_config();