Variable not recognized inside if statement when declared as a block parameter

[masak]

$ perl6 bin/007 -e="if [1, 2, 3] -> a { say(a) }"
Variable 'a' is not declared
  in method find at /home/masak/mine/007/lib/_007/Runtime.pm:74
  in method get-var at /home/masak/mine/007/lib/_007/Runtime.pm:83
  in method eval at /home/masak/mine/007/lib/_007/Q.pm:69
  in method dispatch:<hyper> at src/gen/m-CORE.setting:1351
  in method eval at /home/masak/mine/007/lib/_007/Q.pm:196
  in method run at /home/masak/mine/007/lib/_007/Q.pm:243
  in method run at /home/masak/mine/007/lib/_007/Q.pm:438
  in method run at /home/masak/mine/007/lib/_007/Q.pm:261
  in method run at /home/masak/mine/007/lib/_007/Q.pm:438
  in method run at /home/masak/mine/007/lib/_007/Runtime.pm:28
  in sub run_007 at bin/007:8
  in sub MAIN at bin/007:15
  in sub MAIN at bin/007:11
  in block <unit> at bin/007:15

Closable with a fix and a regression test.

[masak]

I was sure we had a test for this. And we do, in corner-cases.t.

{
    my $program = q:to/./;
        if "James" -> s {
            say(s);
        }
        .

    my $ast = q:to/./;
        (statements
          (if (str "James") (block (parameters (ident "s")) (statements
            (stexpr (call (ident "say") (arguments (ident "s"))))))))
        .

    parses-to $program, $ast, "if statement with a pointy block";
}

But the test only makes sure we compile to the right AST. Something must be going wrong after that. Perhaps in the way Q::Statement::If handles its parameter declaration?