diff --git a/src/tools/ceph-dencoder/ceph_dencoder.cc b/src/tools/ceph-dencoder/ceph_dencoder.cc
index a278e08629f..24640f9b51d 100644
--- a/src/tools/ceph-dencoder/ceph_dencoder.cc
+++ b/src/tools/ceph-dencoder/ceph_dencoder.cc
@@ -49,6 +49,7 @@ void usage(ostream &out)
   out << "  skip <num>          skip <num> leading bytes before decoding\n";
   out << "  decode              decode into in-memory object\n";
   out << "  encode              encode in-memory object\n";
+  out << "  add_crc32c          calculate and encode crc32c for in-memory object\n";
   out << "  dump_json           dump in-memory object as json (to stdout)\n";
   out << "  hexdump             print encoded data in hex\n";
   out << "  get_struct_v        print version of the encoded object\n";
@@ -163,6 +164,16 @@ int main(int argc, const char **argv)
 	return 1;
       }
       den->encode(encbl, features | CEPH_FEATURE_RESERVED); // hack for OSDMap
+    } else if (*i == string("add_crc32c")) {
+      if (!encbl.length()) {
+	cerr << "must first encode something" << std::endl;
+	return 1;
+      }
+      auto p = encbl.begin();
+      ceph_assert(skip < encbl.length());
+      p += skip;
+      __u32 crc = p.crc32c(encbl.length() - skip, 0);
+      encode(crc, encbl);
     } else if (*i == string("decode")) {
       if (!den) {
 	cerr << "must first select type with 'type <name>'" << std::endl;