diff --git a/lib/isc/xoshiro128starstar.c b/lib/isc/xoshiro128starstar.c
index e44b8c022e..a737bfd91c 100644
--- a/lib/isc/xoshiro128starstar.c
+++ b/lib/isc/xoshiro128starstar.c
@@ -34,7 +34,7 @@
  *
  * The state must be seeded so that it is not everywhere zero.
  */
-
+#if defined(ISC_PLATFORM_USETHREADS)
 #if defined(_WIN32) || defined(_WIN64)
 #include <windows.h>
 static volatile HANDLE _mutex = NULL;
@@ -62,6 +62,10 @@ static pthread_mutex_t _mutex = PTHREAD_MUTEX_INITIALIZER;
 #define _LOCK()   pthread_mutex_lock(&_mutex)
 #define _UNLOCK() pthread_mutex_unlock(&_mutex)
 #endif /* defined(_WIN32) || defined(_WIN64) */
+#else /* defined(ISC_PLATFORM_USETHREADS) */
+#define _LOCK()
+#define _UNLOCK()
+#endif
 
 static inline isc_uint32_t rotl(const isc_uint32_t x, int k) {
 	return (x << k) | (x >> (32 - k));