diff --git a/src/kernel/syscall.s b/src/kernel/syscall.s
index b95878b..659bbf4 100644
--- a/src/kernel/syscall.s
+++ b/src/kernel/syscall.s
@@ -23,9 +23,11 @@ syscall_handler_prelude:
 	mov rbp, rsp
 
 	; account for the hole in the sysv abi
-	; argument list since SYSCALL uses rcx
-	mov rcx, r8
-	mov r8, r9
+	; argument list since SYSCALL uses rcx.
+	; r10 is non-preserved but not part of
+	; the function call ABI, so the rcx arg
+	; was stashed there.
+	mov rcx, r10
 
 	push rbx
 	push r11
diff --git a/src/libraries/libc/arch/x86_64/syscalls.s b/src/libraries/libc/arch/x86_64/syscalls.s
index 4a9e42e..b9b5416 100644
--- a/src/libraries/libc/arch/x86_64/syscalls.s
+++ b/src/libraries/libc/arch/x86_64/syscalls.s
@@ -5,9 +5,10 @@
 		mov rbp, rsp
 
 		; args should already be in rdi, etc, but rcx will
-		; get stomped, so shift args out one spot from rcx
-		mov r9, r8
-		mov r8, rcx
+		; get stomped, so stash it in r10, which isn't a
+		; callee-saved register, but also isn't used in the
+		; function call ABI.
+		mov r10, rcx
 
 		mov rax, %2
 		syscall