diff --git a/feed/history/boost_1_80_0.qbk b/feed/history/boost_1_80_0.qbk
index e194bc49..9b4be007 100644
--- a/feed/history/boost_1_80_0.qbk
+++ b/feed/history/boost_1_80_0.qbk
@@ -38,6 +38,8 @@ in the release.
 * Unordered
   * Containers are not in a valid state after moving, see [github unordered 139].
     [@/patches/1_80_0/0003-unordered-valid-after-move.patch Patch].
+  * Fix MSVC /RTCc build runtime failures.
+    [@/patches/1_80_0/0006-unordered-msvc-rtcc.patch Patch].
 
 [endsect]
 
diff --git a/patches/1_80_0/0006-unordered-msvc-rtcc.patch b/patches/1_80_0/0006-unordered-msvc-rtcc.patch
new file mode 100644
index 00000000..1bf17ffa
--- /dev/null
+++ b/patches/1_80_0/0006-unordered-msvc-rtcc.patch
@@ -0,0 +1,19 @@
+diff -ur boost_1_80_0/boost/unordered/detail/prime_fmod.hpp boost_1_80_1/boost/unordered/detail/prime_fmod.hpp
+--- boost_1_80_0/boost/unordered/detail/prime_fmod.hpp	2022-08-03 22:47:16.000000000 -0400
++++ boost_1_80_1/boost/unordered/detail/prime_fmod.hpp	2022-12-14 01:45:27.368620146 -0500
+@@ -117,9 +117,15 @@
+ #if defined(BOOST_UNORDERED_FCA_HAS_64B_SIZE_T)
+           std::size_t sizes_under_32bit = inv_sizes32_len;
+           if (BOOST_LIKELY(size_index < sizes_under_32bit)) {
++#if defined(__MSVC_RUNTIME_CHECKS)
++            return fast_modulo(
++              boost::uint32_t(hash & 0xffffffffu) + boost::uint32_t(hash >> 32),
++              inv_sizes32[size_index], boost::uint32_t(sizes[size_index]));
++#else
+             return fast_modulo(
+               boost::uint32_t(hash) + boost::uint32_t(hash >> 32),
+               inv_sizes32[size_index], boost::uint32_t(sizes[size_index]));
++#endif
+           } else {
+             return positions[size_index - sizes_under_32bit](hash);
+           }
diff --git a/patches/index.html b/patches/index.html
index 383f4b54..b642255e 100644
--- a/patches/index.html
+++ b/patches/index.html
@@ -41,6 +41,7 @@ https://www.boost.org/development/website_updating.html
               <li><a href="1_80_0/0003-unordered-valid-after-move.patch">0003-unordered-valid-after-move.patch</a></li>
               <li><a href="1_80_0/0004-filesystem-posix-fix-no-at-apis-missing-include.patch">0004-filesystem-posix-fix-no-at-apis-missing-include.patch</a></li>
               <li><a href="1_80_0/0005-config-libcpp15.patch">0005-config-libcpp15.patch</a></li>
+              <li><a href="1_80_0/0006-unordered-msvc-rtcc.patch">0006-unordered-msvc-rtcc.patch</a></li>
             </ul>
 
             <h2>1.79.0</h2>