diff --git a/src/swap.s b/src/swap.s
index 01b2e70..da9dcd1 100644
--- a/src/swap.s
+++ b/src/swap.s
@@ -31,6 +31,8 @@ jmp 2f
   movq %rax, %rsp
 
   // jump into the new context (return to the call point)
+  // doing this instead of a straight `ret` is 8ns slower,
+  // presumably because the branch predictor tries to be clever about it
   popq %rax
   jmpq *%rax