diff --git a/src/vm/jvm/QAST/Compiler.nqp b/src/vm/jvm/QAST/Compiler.nqp
index 6eef385a7f..9d0f3c98d5 100644
--- a/src/vm/jvm/QAST/Compiler.nqp
+++ b/src/vm/jvm/QAST/Compiler.nqp
@@ -2845,7 +2845,7 @@ QAST::OperationsJAST.map_classlib_core_op('jvmgetproperties', $TYPE_OPS, 'jvmget
 QAST::OperationsJAST.map_classlib_core_op('getrusage', $TYPE_OPS, 'getrusage', [$RT_OBJ], $RT_OBJ, :tc);
 
 # thread related opcodes
-QAST::OperationsJAST.map_classlib_core_op('newthread', $TYPE_OPS, 'newthread', [$RT_OBJ, $RT_INT], $RT_OBJ, :tc);
+QAST::OperationsJAST.map_classlib_core_op('newthread', $TYPE_OPS, 'newthread', [$RT_OBJ, $RT_INT, $RT_INT], $RT_OBJ, :tc);
 QAST::OperationsJAST.map_classlib_core_op('threadrun', $TYPE_OPS, 'threadrun', [$RT_OBJ], $RT_OBJ, :tc);
 QAST::OperationsJAST.map_classlib_core_op('threadjoin', $TYPE_OPS, 'threadjoin', [$RT_OBJ], $RT_OBJ, :tc);
 QAST::OperationsJAST.map_classlib_core_op('threadid', $TYPE_OPS, 'threadid', [$RT_OBJ], $RT_INT, :tc);
diff --git a/src/vm/jvm/runtime/org/perl6/nqp/runtime/Ops.java b/src/vm/jvm/runtime/org/perl6/nqp/runtime/Ops.java
index a58dac11e6..fb5276cbae 100644
--- a/src/vm/jvm/runtime/org/perl6/nqp/runtime/Ops.java
+++ b/src/vm/jvm/runtime/org/perl6/nqp/runtime/Ops.java
@@ -5706,9 +5706,9 @@ public void run() {
             invokeArgless(tc, code);
         }
     }
-    public static SixModelObject newthread(SixModelObject code, long appLifetime, ThreadContext tc) {
+    public static SixModelObject newthread(SixModelObject code, long appLifetime, long stackSize, ThreadContext tc) {
         SixModelObject thread = tc.gc.Thread.st.REPR.allocate(tc, tc.gc.Thread.st);
-        ((VMThreadInstance)thread).thread = new Thread(new CodeRunnable(tc.gc, thread, code));
+        ((VMThreadInstance)thread).thread = new Thread(new CodeRunnable(tc.gc, thread, code, stackSize));
         ((VMThreadInstance)thread).thread.setDaemon(appLifetime != 0);
         return thread;
     }
diff --git a/t/concurrency/01-thread.t b/t/concurrency/01-thread.t
index 9979cbb560..775a488e37 100644
--- a/t/concurrency/01-thread.t
+++ b/t/concurrency/01-thread.t
@@ -3,7 +3,7 @@ plan(24);
 # 2 tests
 {
     my $ran := 0;
-    my $t   := nqp::newthread({ $ran := 1 }, 0);
+    my $t   := nqp::newthread({ $ran := 1 }, 0, 0);
     ok(nqp::defined($t), 'Can create a new non-app-lifetime thread');
     nqp::threadrun($t);
     nqp::threadjoin($t);
@@ -13,7 +13,7 @@ plan(24);
 # 2 tests
 {
     my $start := nqp::time_n();
-    my $t     := nqp::newthread({ nqp::sleep(10.0) }, 1);
+    my $t     := nqp::newthread({ nqp::sleep(10.0) }, 1, 0);
     ok(nqp::defined($t), 'Can create a new app-lifetime thread');
     nqp::threadrun($t);
     ok(nqp::time_n() - $start < 10.0,
@@ -26,7 +26,7 @@ plan(24);
     my $t := nqp::newthread({
         1 until $done;
         ok(1, 'Can write to STDOUT in child thread');
-    }, 0);
+    }, 0, 0);
     ok(1, 'Can write to STDOUT in parent thread before threadrun');
     nqp::threadrun($t);
     ok(1, 'Can write to STDOUT in parent thread after threadrun');
@@ -45,7 +45,7 @@ plan(24);
     my $cid := 0;
     my $t   := nqp::newthread({
         $cid := nqp::threadid(nqp::currentthread());
-    }, 0);
+    }, 0, 0);
     ok(nqp::defined($t), 'Can create another new thread after previous joins');
 
     $tid := nqp::threadid($t);
@@ -69,8 +69,8 @@ plan(24);
 {
     my $a  := 0;
     my $b  := 0;
-    my $t1 := nqp::newthread({ $a := 21 }, 0);
-    my $t2 := nqp::newthread({ $b := 42 }, 0);
+    my $t1 := nqp::newthread({ $a := 21 }, 0, 0);
+    my $t2 := nqp::newthread({ $b := 42 }, 0, 0);
 
     nqp::threadrun($t1);
     nqp::threadrun($t2);
@@ -96,7 +96,7 @@ plan(24);
         nqp::push(@a, '1');
         nqp::threadyield() until nqp::elems(@a) == 3 && @a[2] eq 'b';
         nqp::push(@a, '2');
-    }, 0);
+    }, 0, 0);
 
     # Make sure child thread is at least *runnable* (if not actually running)
     # before running parent thread's code.
@@ -133,13 +133,13 @@ plan(24);
         nqp::push(@a, 'b');
         nqp::threadyield() until nqp::elems(@a) == 4 && @a[3] eq '2';
         nqp::push(@a, 'c');
-    }, 0);
+    }, 0, 0);
     my $t2 := nqp::newthread({
         nqp::threadyield() until nqp::elems(@a) == 1 && @a[0] eq 'a';
         nqp::push(@a, '1');
         nqp::threadyield() until nqp::elems(@a) == 3 && @a[2] eq 'b';
         nqp::push(@a, '2');
-    }, 0);
+    }, 0, 0);
 
     # Make sure $t2 is at least *runnable* (if not actually running)
     # before $t1 becomes runnable.
diff --git a/t/concurrency/02-lock.t b/t/concurrency/02-lock.t
index aab687f948..2b083e1905 100644
--- a/t/concurrency/02-lock.t
+++ b/t/concurrency/02-lock.t
@@ -45,7 +45,7 @@ my class CondVar is repr('ConditionVariable') { }
         nqp::lock($l);
         ok(1, 'Lock that survived CATCH works in another thread too');
         nqp::unlock($l);
-    }, 0);
+    }, 0, 0);
     nqp::threadrun($t);
     nqp::threadjoin($t);
 
@@ -70,7 +70,7 @@ my class CondVar is repr('ConditionVariable') { }
             $output := $output ~ 'a';
         }
         nqp::unlock($l);
-    }, 0);
+    }, 0, 0);
 
     my $t2     := nqp::newthread({
         nqp::lock($l);
@@ -79,7 +79,7 @@ my class CondVar is repr('ConditionVariable') { }
             $output := $output ~ 'b';
         }
         nqp::unlock($l);
-    }, 0);
+    }, 0, 0);
 
     nqp::threadrun($t1);
     nqp::threadrun($t2);
@@ -111,7 +111,7 @@ my class CondVar is repr('ConditionVariable') { }
         nqp::condsignalall($c);
         $now1 := nqp::time_n();
         nqp::unlock($l);
-    }, 0);
+    }, 0, 0);
     nqp::threadrun($t1);
 
     my $elems := 0;
@@ -130,7 +130,7 @@ my class CondVar is repr('ConditionVariable') { }
         }
         nqp::push(@log, 'lager');
         nqp::unlock($l);
-    }, 0);
+    }, 0, 0);
     nqp::threadrun($t2);
 
     nqp::threadjoin($t1);
@@ -161,35 +161,35 @@ my class CondVar is repr('ConditionVariable') { }
         nqp::condsignalone($c1);
         nqp::condsignalall($c2);
         nqp::unlock($l);
-    }, 0);
+    }, 0, 0);
 
     my $t2 := nqp::newthread({
         nqp::lock($l);
         nqp::condwait($c1);
         $count_one++;
         nqp::unlock($l);
-    }, 0);
+    }, 0, 0);
 
     my $t3 := nqp::newthread({
         nqp::lock($l);
         nqp::condwait($c1);
         $count_one++;
         nqp::unlock($l);
-    }, 0);
+    }, 0, 0);
 
     my $t4 := nqp::newthread({
         nqp::lock($l);
         nqp::condwait($c2);
         $count_all++;
         nqp::unlock($l);
-    }, 0);
+    }, 0, 0);
 
     my $t5 := nqp::newthread({
         nqp::lock($l);
         nqp::condwait($c2);
         $count_all++;
         nqp::unlock($l);
-    }, 0);
+    }, 0, 0);
 
     # Start all waiting threads
     nqp::threadrun($t2);
diff --git a/t/concurrency/03-semaphore.t b/t/concurrency/03-semaphore.t
index bd7c73012b..acde22f3c0 100644
--- a/t/concurrency/03-semaphore.t
+++ b/t/concurrency/03-semaphore.t
@@ -38,28 +38,28 @@ my class Semaphore is repr('Semaphore') { }
     my $s  := nqp::box_i(3, Semaphore);
     my $t1 := nqp::newthread({
         nqp::semacquire($s);
-    }, 0);
+    }, 0, 0);
     my $t2 := nqp::newthread({
         nqp::semacquire($s);
-    }, 0);
+    }, 0, 0);
     my $t3 := nqp::newthread({
         nqp::semacquire($s);
-    }, 0);
+    }, 0, 0);
     my $t4 := nqp::newthread({
         ok(!nqp::semtryacquire($s), 'Trying fourth acquire before release fails');
-    }, 0);
+    }, 0, 0);
     my $t5 := nqp::newthread({
         my $before := nqp::time_n();
         nqp::semacquire($s);
         my $after  := nqp::time_n();
         ok($after - $before > 1.0, 'Fourth acquire blocks on empty semaphore');
         ok($released, 'Fourth acquire succeeds after release in other thread');
-    }, 0);
+    }, 0, 0);
     my $t6 := nqp::newthread({
         nqp::sleep(3.0);
         $released := 1;
         nqp::semrelease($s);
-    }, 0);
+    }, 0, 0);
 
     # First, exhaust semaphore capacity
     nqp::threadrun($t1);
diff --git a/t/concurrency/04-osr-crash.t b/t/concurrency/04-osr-crash.t
index 027a5021c5..477e4029d8 100644
--- a/t/concurrency/04-osr-crash.t
+++ b/t/concurrency/04-osr-crash.t
@@ -9,7 +9,7 @@ my $t := nqp::newthread({
         ok(1, "in thread");
         dec()
     }
-}, 1);
+}, 1, 0);
 nqp::threadrun($t);
 nqp::threadjoin($t);
 ok(1, "Thread with top level loop survived");