diff --git a/base/crypto/signature_creator_nss.cc b/base/crypto/signature_creator_nss.cc
index 7108975934cd7f84de5e9f95e582ceae94244e80..e0de4b7880692f5b4249c103fc12952608e6b6e8 100644
--- a/base/crypto/signature_creator_nss.cc
+++ b/base/crypto/signature_creator_nss.cc
@@ -47,6 +47,8 @@ SignatureCreator::~SignatureCreator() {
 }
 
 bool SignatureCreator::Update(const uint8* data_part, int data_part_len) {
+  // TODO(wtc): Remove this const_cast when we require NSS 3.12.5.
+  // See NSS bug https://bugzilla.mozilla.org/show_bug.cgi?id=518255
   SECStatus rv = SGN_Update(sign_context_,
                             const_cast<unsigned char*>(data_part),
                             data_part_len);