diff -Naur ceph-14.2.8.orig/CMakeLists.txt ceph-14.2.8/CMakeLists.txt
--- ceph-14.2.8.orig/CMakeLists.txt	2020-03-02 18:49:20.000000000 +0100
+++ ceph-14.2.8/CMakeLists.txt	2020-04-08 18:01:17.060097883 +0200
@@ -150,6 +150,8 @@
 CHECK_TYPE_SIZE(__s16 __S16) 
 CHECK_TYPE_SIZE(__s32 __S32) 
 CHECK_TYPE_SIZE(__s64 __S64) 
+CHECK_TYPE_SIZE(size_t SIZE_SIZE_T)
+CHECK_TYPE_SIZE(unsigned SIZE_UNSIGNED)
 unset(CMAKE_EXTRA_INCLUDE_FILES)
 
 include(CheckSymbolExists)
diff -Naur ceph-14.2.8.orig/src/include/buffer.h ceph-14.2.8/src/include/buffer.h
--- ceph-14.2.8.orig/src/include/buffer.h	2020-03-02 18:49:20.000000000 +0100
+++ ceph-14.2.8/src/include/buffer.h	2020-04-08 18:01:55.099897524 +0200
@@ -737,7 +737,9 @@
 
       void advance(int o) = delete;
       void advance(unsigned o);
+#if SIZE_SIZE_T != SIZE_UNSIGNED
       void advance(size_t o) { advance(static_cast<unsigned>(o)); }
+#endif
       void seek(unsigned o);
       char operator*() const;
       iterator_impl& operator++();
diff -Naur ceph-14.2.8.orig/src/include/config-h.in.cmake ceph-14.2.8/src/include/config-h.in.cmake
--- ceph-14.2.8.orig/src/include/config-h.in.cmake	2020-03-02 18:49:20.000000000 +0100
+++ ceph-14.2.8/src/include/config-h.in.cmake	2020-04-08 18:01:33.360012038 +0200
@@ -81,6 +81,12 @@
 /* Define to 1 if the system has the type `__u8'. */
 #cmakedefine HAVE___U8 1
 
+/* Size of `size_t` */
+#cmakedefine SIZE_SIZE_T @SIZE_SIZE_T@
+
+/* Size of `unsigned` */
+#cmakedefine SIZE_UNSIGNED @SIZE_UNSIGNED@
+
 /* Define if you have res_nquery */
 #cmakedefine HAVE_RES_NQUERY