diff --git a/arch/risc-v/src/common/fork.S b/arch/risc-v/src/common/fork.S
index 37d4bc9cfe..9070e93b21 100644
--- a/arch/risc-v/src/common/fork.S
+++ b/arch/risc-v/src/common/fork.S
@@ -117,8 +117,8 @@ up_fork:
   REGSTORE    s0, FORK_S0_OFFSET(sp)
 #endif
 
-  addi        s0, sp, FORK_SIZEOF
-  REGSTORE    s0, FORK_SP_OFFSET(sp) /* original SP */
+  addi        a0, sp, FORK_SIZEOF
+  REGSTORE    a0, FORK_SP_OFFSET(sp) /* original SP */
   REGSTORE    x1, FORK_RA_OFFSET(sp) /* return address */
 
   /* Floating point registers */