diff --git a/lib/isc/win32/include/isc/mutex.h b/lib/isc/win32/include/isc/mutex.h
index dc8786996f..a258c82f65 100644
--- a/lib/isc/win32/include/isc/mutex.h
+++ b/lib/isc/win32/include/isc/mutex.h
@@ -20,8 +20,11 @@
 
 #include <windows.h>
 
+#include <isc/lang.h>
 #include <isc/result.h>
 
+ISC_LANG_BEGINDECLS
+
 typedef CRITICAL_SECTION isc_mutex_t;
 
 #define isc_mutex_init(mp) \
@@ -35,4 +38,6 @@ typedef CRITICAL_SECTION isc_mutex_t;
 #define isc_mutex_destroy(mp) \
 	(DeleteCriticalSection((mp)), ISC_R_SUCCESS)
 
+ISC_LANG_ENDDECLS
+
 #endif /* ISC_MUTEX_H */