diff --git a/twasm/asm/main.asm b/twasm/asm/main.asm
index c371189..75a7c33 100644
--- a/twasm/asm/main.asm
+++ b/twasm/asm/main.asm
@@ -1348,6 +1348,7 @@ get_reg_bits:
 ; ------------------------------------------------------------------------------
 
 tokenise:
+  mov rbp, rsp
                ; rdi -> current byte of program
   xor eax, eax ; rax = number of tokens processed
   xor edx, edx ; dl = current byte of program
@@ -1654,6 +1655,7 @@ tokenise:
     jmp .loop
 
   .break:
+    mov rsp, rbp
     ret
 
   ; state