diff --git a/src/core/ThreadPoolScheduler.pm6 b/src/core/ThreadPoolScheduler.pm6
index 367901430ab..209a2d315c3 100644
--- a/src/core/ThreadPoolScheduler.pm6
+++ b/src/core/ThreadPoolScheduler.pm6
@@ -320,66 +320,85 @@ my class ThreadPoolScheduler does Scheduler {
     has Thread $!supervisor;
 
     method !general-queue() {
-        unless $!general-queue.DEFINITE {
-            $!state-lock.protect: {
-                unless $!general-queue.DEFINITE {
+        nqp::if(
+          nqp::isconcrete($!general-queue),
+          $!general-queue,
+          nqp::stmts(
+            $!state-lock.protect( {
+                nqp::unless(
+                  nqp::isconcrete($!general-queue),
+                  nqp::stmts(
                     # We don't have any workers yet, so start one.
-                    $!general-queue := nqp::create(Queue);
-                    $!general-workers := first-worker(
+                    ($!general-queue := nqp::create(Queue)),
+                    ($!general-workers := first-worker(
                       GeneralWorker.new(
                         queue => $!general-queue,
                         scheduler => self
                       )
-                    );
-                    scheduler-debug "Created initial general worker thread";
-                    self!maybe-start-supervisor();
-                }
-            }
-        }
-        $!general-queue
+                    )),
+                    scheduler-debug("Created initial general worker thread"),
+                    self!maybe-start-supervisor
+                  )
+                )
+            } ),
+            $!general-queue
+          )
+        )
     }
 
     method !timer-queue() {
-        unless $!timer-queue.DEFINITE {
-            $!state-lock.protect: {
-                unless $!timer-queue.DEFINITE {
+        nqp::if(
+          nqp::isconcrete($!timer-queue),
+          $!timer-queue,
+          nqp::stmts(
+            $!state-lock.protect( {
+                nqp::unless(
+                  nqp::isconcrete($!timer-queue),
+                  nqp::stmts(
                     # We don't have any workers yet, so start one.
-                    $!timer-queue := nqp::create(Queue);
-                    $!timer-workers := first-worker(
+                    ($!timer-queue := nqp::create(Queue)),
+                    ($!timer-workers := first-worker(
                       TimerWorker.new(
                         queue => $!timer-queue,
                         scheduler => self
                       )
-                    );
-                    scheduler-debug "Created initial timer worker thread";
-                    self!maybe-start-supervisor();
-                }
-            }
-        }
-        $!timer-queue
+                    )),
+                    scheduler-debug("Created initial general worker thread"),
+                    self!maybe-start-supervisor
+                  )
+                )
+            } ),
+            $!timer-queue
+          )
+        )
     }
 
     constant @affinity-add-thresholds = 1, 5, 10, 20, 50, 100;
     method !affinity-queue() {
         # If there's no affinity workers, start one.
-        my $cur-affinity-workers := $!affinity-workers;
-        if $cur-affinity-workers.elems == 0 {
-            $!state-lock.protect: {
-                if $!affinity-workers.elems == 0 {
+        nqp::unless(
+          nqp::elems(my $cur-affinity-workers := $!affinity-workers),
+          nqp::stmts(
+            $!state-lock.protect( {
+                nqp::unless(
+                  nqp::elems($!affinity-workers),
+                  nqp::stmts(
                     # We don't have any affinity workers yet, so start one
                     # and return its queue.
-                    $!affinity-workers := first-worker(
+                    ($!affinity-workers := first-worker(
                       AffinityWorker.new(
                         scheduler => self
                       )
-                    );
-                    scheduler-debug "Created initial affinity worker thread";
-                    self!maybe-start-supervisor();
-                    return $!affinity-workers[0].queue;
-                }
-            }
-            $cur-affinity-workers := $!affinity-workers; # lost race for first
-        }
+                    )),
+                    scheduler-debug("Created initial affinity worker thread"),
+                    self!maybe-start-supervisor,
+                    (return $!affinity-workers[0].queue)
+                  )
+                )
+            } ),
+            ($cur-affinity-workers := $!affinity-workers) # lost race for first
+          )
+        );
 
         # Otherwise, see which has the least load (this is inherently racey
         # and approximate, but enough to help us avoid a busy worker). If we
@@ -387,17 +406,23 @@ my class ThreadPoolScheduler does Scheduler {
         my $most-free-worker;
         my int $i = -1;
         nqp::while(
-          ++$i < nqp::elems($cur-affinity-workers),
+          nqp::islt_i(
+            ($i = nqp::add_i($i,1)),
+            nqp::elems($cur-affinity-workers)
+          ),
           nqp::if(
-            $most-free-worker.DEFINITE,
+            nqp::isconcrete($most-free-worker),
             nqp::stmts(
               (my $cand := nqp::atpos($cur-affinity-workers,$i)),
               nqp::unless(
-                (my $queue := $cand.queue).elems,
+                nqp::elems(my $queue := $cand.queue),
                 (return $queue)
               ),
               nqp::if(
-                nqp::islt_i($queue.elems,$most-free-worker.queue.elems),
+                nqp::islt_i(
+                  nqp::elems($queue),
+                  nqp::elems($most-free-worker.queue)
+                ),
                 $most-free-worker := $cand
               )
             ),