diff --git a/libcxx/src/atomic.cpp b/libcxx/src/atomic.cpp
--- a/libcxx/src/atomic.cpp
+++ b/libcxx/src/atomic.cpp
@@ -16,6 +16,9 @@
 #include <iostream>
 
 #ifdef __linux__
+#if !defined(__NR_futex) && defined(__riscv) && __riscv_xlen == 32
+# define __NR_futex __NR_futex_time64
+#endif
 
 #include <unistd.h>
 #include <linux/futex.h>