diff --git a/src/job.c b/src/job.c
index 587b0b4..ae30d4a 100644
--- a/src/job.c
+++ b/src/job.c
@@ -59,7 +59,7 @@ __attribute__((noreturn)) static void run_vm(void) {
 
 static void *job_start_(const uint32_t entry_point) {
     term_kprint("allocate new stack...");
-    static const int job_stack_size = 64 * 1024; // 64 kiB stack
+    static const int job_stack_size = 48 * 1024; // 48 kiB stack
     const uint32_t child_stack = (uint32_t)kmalloc(job_stack_size, NULL);
     const uint32_t new_sp = ((child_stack + 3) >> 2 << 2) + ((job_stack_size + 3) >> 2 << 2);
     term_kprintf("new_bp=0x%08x", child_stack);
@@ -102,6 +102,8 @@ void job_resume(int job_id) {
     wrenResume(job_vms[job_id]); // longjmp(vm->ctxbuf, 1);
 }
 
+void job_GC(int job_id) { wrenCollectGarbage(job_vms[job_id]); }
+
 void job_free(int job_id) {
     // just in case something failed
     if (job_vms[job_id] != NULL) {
diff --git a/src/job.h b/src/job.h
index 35982a1..c985079 100644
--- a/src/job.h
+++ b/src/job.h
@@ -11,6 +11,7 @@ extern void *job_stacks[UNS_MAX_JOBS];
 extern int current_job_id;
 
 int job_start(const char *name, const char *source);
+void job_GC(int job_id);
 void job_resume(int job_id);
 void job_free(int job_id);
 
diff --git a/src/main.c b/src/main.c
index 0d464f1..1c1c4ec 100644
--- a/src/main.c
+++ b/src/main.c
@@ -124,6 +124,16 @@ int main(int isappli, int optnum) {
                             "}\n"
                             "System.print(\"inner end\")\n");
 
+    job_start("test_job_3", "System.print(\"inner start\")\n"
+                            "var i = 0\n"
+                            "while (i < 30000) {\n"
+                            "    if ((i % 500) == 0) {\n"
+                            "        System.write(\"vm 3: i=%(i)\\n\")\n"
+                            "    }\n"
+                            "    i = i + 1\n"
+                            "}\n"
+                            "System.print(\"inner end\")\n");
+
     while (1) {
         // system routine
 
@@ -165,6 +175,7 @@ int main(int isappli, int optnum) {
             must_yield = 0;
             job_resume(current_job_id);
         } else if (ret == 1) {
+            job_GC(current_job_id);
             // term_kprintf("job(%d) yield", current_job_id);
             continue;
         } else if (ret == 2) {