diff --git a/configure.ac b/configure.ac
index e317d0a..b58aa52 100644
--- a/configure.ac
+++ b/configure.ac
@@ -292,13 +292,22 @@
   JEMALLOC_CPREFIX=`echo ${JEMALLOC_PREFIX} | tr "a-z" "A-Z"`
   AC_DEFINE_UNQUOTED([JEMALLOC_PREFIX], ["$JEMALLOC_PREFIX"])
   AC_DEFINE_UNQUOTED([JEMALLOC_CPREFIX], ["$JEMALLOC_CPREFIX"])
-  jemalloc_prefix="$JEMALLOC_PREFIX"
-  jemalloc_cprefix="$JEMALLOC_CPREFIX"
-  AC_SUBST([jemalloc_prefix])
-  AC_SUBST([jemalloc_cprefix])
   AC_DEFINE_UNQUOTED([JEMALLOC_P(string_that_no_one_should_want_to_use_as_a_jemalloc_API_prefix)], [${JEMALLOC_PREFIX}##string_that_no_one_should_want_to_use_as_a_jemalloc_API_prefix])
 fi
 
+dnl Do not mangle library-private APIs by default.
+AC_ARG_WITH([private_namespace],
+  [AS_HELP_STRING([--with-private-namespace=<prefix>], [Prefix to prepend to all library-private APIs])],
+  [JEMALLOC_PRIVATE_NAMESPACE="$with_private_namespace"],
+  [JEMALLOC_PRIVATE_NAMESPACE=""]
+)
+AC_DEFINE_UNQUOTED([JEMALLOC_PRIVATE_NAMESPACE], ["$JEMALLOC_PRIVATE_NAMESPACE"])
+if test "x$JEMALLOC_PRIVATE_NAMESPACE" != "x" ; then
+  AC_DEFINE_UNQUOTED([JEMALLOC_N(string_that_no_one_should_want_to_use_as_a_jemalloc_private_namespace_prefix)], [${JEMALLOC_PRIVATE_NAMESPACE}##string_that_no_one_should_want_to_use_as_a_jemalloc_private_namespace_prefix])
+else
+  AC_DEFINE_UNQUOTED([JEMALLOC_N(string_that_no_one_should_want_to_use_as_a_jemalloc_private_namespace_prefix)], [string_that_no_one_should_want_to_use_as_a_jemalloc_private_namespace_prefix])
+fi
+
 dnl Do not add suffix to installed files by default.
 AC_ARG_WITH([install_suffix],
   [AS_HELP_STRING([--with-install-suffix=<suffix>], [Suffix to append to all installed files])],
@@ -905,6 +914,8 @@
 AC_MSG_RESULT([abs_objroot        : ${abs_objroot}])
 AC_MSG_RESULT([])
 AC_MSG_RESULT([JEMALLOC_PREFIX    : ${JEMALLOC_PREFIX}])
+AC_MSG_RESULT([JEMALLOC_PRIVATE_NAMESPACE])
+AC_MSG_RESULT([                   : ${JEMALLOC_PRIVATE_NAMESPACE}])
 AC_MSG_RESULT([install_suffix     : ${install_suffix}])
 AC_MSG_RESULT([autogen            : ${enable_autogen}])
 AC_MSG_RESULT([cc-silence         : ${enable_cc_silence}])