diff --git a/cmake/Libraries.cmake b/cmake/Libraries.cmake
index 28f85ba39..2c2dcea2a 100644
--- a/cmake/Libraries.cmake
+++ b/cmake/Libraries.cmake
@@ -228,7 +228,6 @@ macro(configure_unix_libs)
 
   # For config.h, set some static values; it may be a good idea to make these
   # values dynamic for non-standard UNIX compilers.
-  set(HAVE_CXX_MUTABLE 1)
   set(HAVE_CXX_STDLIB 1)
   set(HAVE_PTHREAD_SIGNAL 1)
   set(SELECT_TYPE_ARG1 int)
diff --git a/src/lib/config.h.in b/src/lib/config.h.in
index 93ba46c08..a802ce5b4 100644
--- a/src/lib/config.h.in
+++ b/src/lib/config.h.in
@@ -17,9 +17,6 @@
 
 // clang-format off
 
-/* Define if your compiler has mutable support. */
-#cmakedefine HAVE_CXX_MUTABLE @HAVE_CXX_MUTABLE@
-
 /* Define if your compiler has standard C++ library support. */
 #cmakedefine HAVE_CXX_STDLIB @HAVE_CXX_STDLIB@