diff --git a/lib/isc/Makefile.am b/lib/isc/Makefile.am
index fb443b5d6e..b61c8c88f2 100644
--- a/lib/isc/Makefile.am
+++ b/lib/isc/Makefile.am
@@ -154,6 +154,7 @@ libisc_la_SOURCES =		\
 	mem_p.h			\
 	meminfo.c		\
 	mutex.c			\
+	mutex_p.h		\
 	mutexblock.c		\
 	net.c			\
 	netaddr.c		\
diff --git a/lib/isc/lib.c b/lib/isc/lib.c
index 7f6b12c4aa..dd42ea792b 100644
--- a/lib/isc/lib.c
+++ b/lib/isc/lib.c
@@ -21,6 +21,7 @@
 
 #include "config.h"
 #include "mem_p.h"
+#include "mutex_p.h"
 #include "os_p.h"
 #include "tls_p.h"
 #include "trampoline_p.h"
@@ -41,6 +42,7 @@ isc__shutdown(void) ISC_DESTRUCTOR;
 void
 isc__initialize(void) {
 	isc__os_initialize();
+	isc__mutex_initialize();
 	isc__mem_initialize();
 	isc__tls_initialize();
 	isc__trampoline_initialize();
@@ -52,5 +54,6 @@ isc__shutdown(void) {
 	isc__trampoline_shutdown();
 	isc__tls_shutdown();
 	isc__mem_shutdown();
+	isc__mutex_shutdown();
 	isc__os_shutdown();
 }
diff --git a/lib/isc/mutex.c b/lib/isc/mutex.c
index a73c276193..075fc37b32 100644
--- a/lib/isc/mutex.c
+++ b/lib/isc/mutex.c
@@ -26,32 +26,36 @@
 #include <isc/string.h>
 #include <isc/util.h>
 
-#ifdef HAVE_PTHREAD_MUTEX_ADAPTIVE_NP
-static bool attr_initialized = false;
-static pthread_mutexattr_t attr;
-static isc_once_t once_attr = ISC_ONCE_INIT;
+#include "mutex_p.h"
+
+pthread_mutexattr_t isc__mutex_init_attr;
+static isc_once_t init_once = ISC_ONCE_INIT;
 
 static void
-initialize_attr(void) {
-	RUNTIME_CHECK(pthread_mutexattr_init(&attr) == 0);
-	RUNTIME_CHECK(pthread_mutexattr_settype(
-			      &attr, PTHREAD_MUTEX_ADAPTIVE_NP) == 0);
-	attr_initialized = true;
-}
+mutex_initialize(void) {
+	RUNTIME_CHECK(pthread_mutexattr_init(&isc__mutex_init_attr) == 0);
+#ifdef HAVE_PTHREAD_MUTEX_ADAPTIVE_NP
+	RUNTIME_CHECK(pthread_mutexattr_settype(&isc__mutex_init_attr,
+						PTHREAD_MUTEX_ADAPTIVE_NP) ==
+		      0);
 #endif /* HAVE_PTHREAD_MUTEX_ADAPTIVE_NP */
+}
+
+void
+isc__mutex_initialize(void) {
+	RUNTIME_CHECK(isc_once_do(&init_once, mutex_initialize) ==
+		      ISC_R_SUCCESS);
+}
 
 void
 isc__mutex_init(isc_mutex_t *mp) {
 	int err;
 
-#ifdef HAVE_PTHREAD_MUTEX_ADAPTIVE_NP
-	isc_result_t result = ISC_R_SUCCESS;
-	result = isc_once_do(&once_attr, initialize_attr);
-	RUNTIME_CHECK(result == ISC_R_SUCCESS);
-
-	err = pthread_mutex_init(mp, &attr);
-#else  /* HAVE_PTHREAD_MUTEX_ADAPTIVE_NP */
-	err = pthread_mutex_init(mp, NULL);
-#endif /* HAVE_PTHREAD_MUTEX_ADAPTIVE_NP */
+	err = pthread_mutex_init(mp, &isc__mutex_init_attr);
 	ERRNO_CHECK(pthread_mutex_init, err);
 }
+
+void
+isc__mutex_shutdown(void) {
+	/* noop */;
+}
diff --git a/lib/isc/mutex_p.h b/lib/isc/mutex_p.h
new file mode 100644
index 0000000000..e9aa8a891b
--- /dev/null
+++ b/lib/isc/mutex_p.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at https://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+#pragma once
+
+/*! \file */
+
+void
+isc__mutex_initialize(void);
+
+void
+isc__mutex_shutdown(void);