diff --git a/src/rt/rust_task.cpp b/src/rt/rust_task.cpp
index 266c0652c6e59..3b6ce56ddab3e 100644
--- a/src/rt/rust_task.cpp
+++ b/src/rt/rust_task.cpp
@@ -54,8 +54,7 @@ rust_task::rust_task(rust_sched_loop *sched_loop, rust_task_state state,
     disallow_yield(0),
     c_stack(NULL),
     next_c_sp(0),
-    next_rust_sp(0),
-    big_stack(NULL)
+    next_rust_sp(0)
 {
     LOGPTR(sched_loop, "new task", (uintptr_t)this);
     DLOG(sched_loop, task, "sizeof(task) = %d (0x%x)",
@@ -564,14 +563,8 @@ rust_task::cleanup_after_turn() {
 
     while (stk->next) {
         stk_seg *new_next = stk->next->next;
-
-        if (stk->next->is_big) {
-            assert (big_stack == stk->next);
-            sched_loop->return_big_stack(big_stack);
-            big_stack = NULL;
-        } else {
-            free_stack(stk->next);
-        }
+        assert (!stk->next->is_big);
+        free_stack(stk->next);
 
         stk->next = new_next;
     }
@@ -581,39 +574,20 @@ rust_task::cleanup_after_turn() {
 // stack and false otherwise.
 bool
 rust_task::new_big_stack() {
-    // If we have a cached big stack segment, use it.
-    if (big_stack) {
-        // Check to see if we're already on the big stack.
-        stk_seg *ss = stk;
-        while (ss != NULL) {
-            if (ss == big_stack)
-                return false;
-            ss = ss->prev;
-        }
-
-        // Unlink the big stack.
-        if (big_stack->next)
-            big_stack->next->prev = big_stack->prev;
-        if (big_stack->prev)
-            big_stack->prev->next = big_stack->next;
-    } else {
-        stk_seg *borrowed_big_stack = sched_loop->borrow_big_stack();
-        if (!borrowed_big_stack) {
-            abort();
-        } else {
-            big_stack = borrowed_big_stack;
-        }
+    stk_seg *borrowed_big_stack = sched_loop->borrow_big_stack();
+    if (!borrowed_big_stack) {
+        return false;
     }
 
-    big_stack->task = this;
-    big_stack->next = stk->next;
-    if (big_stack->next)
-        big_stack->next->prev = big_stack;
-    big_stack->prev = stk;
+    borrowed_big_stack->task = this;
+    borrowed_big_stack->next = stk->next;
+    if (borrowed_big_stack->next)
+        borrowed_big_stack->next->prev = borrowed_big_stack;
+    borrowed_big_stack->prev = stk;
     if (stk)
-        stk->next = big_stack;
+        stk->next = borrowed_big_stack;
 
-    stk = big_stack;
+    stk = borrowed_big_stack;
 
     return true;
 }
@@ -638,10 +612,9 @@ void
 rust_task::reset_stack_limit() {
     uintptr_t sp = get_sp();
     while (!sp_in_stk_seg(sp, stk)) {
-        stk = stk->prev;
+        prev_stack();
         assert(stk != NULL && "Failed to find the current stack");
     }
-    record_stack_limit();
 }
 
 void
@@ -665,8 +638,6 @@ rust_task::delete_all_stacks() {
 
         stk = prev;
     }
-
-    big_stack = NULL;
 }
 
 /*
diff --git a/src/rt/rust_task.h b/src/rt/rust_task.h
index 672af608db863..ac3d3d212dd39 100644
--- a/src/rt/rust_task.h
+++ b/src/rt/rust_task.h
@@ -275,9 +275,6 @@ rust_task : public kernel_owned<rust_task>
     uintptr_t next_c_sp;
     uintptr_t next_rust_sp;
 
-    // The big stack.
-    stk_seg *big_stack;
-
     // Called when the atomic refcount reaches zero
     void delete_this();
 
@@ -604,7 +601,21 @@ rust_task::prev_stack() {
     // require switching to the C stack and be costly. Instead we'll just move
     // up the link list and clean up later, either in new_stack or after our
     // turn ends on the scheduler.
-    stk = stk->prev;
+    if (stk->is_big) {
+        stk_seg *ss = stk;
+        stk = stk->prev;
+
+        // Unlink the big stack.
+        if (ss->next)
+            ss->next->prev = ss->prev;
+        if (ss->prev)
+            ss->prev->next = ss->next;
+
+        sched_loop->return_big_stack(ss);
+    } else {
+        stk = stk->prev;
+    }
+
     record_stack_limit();
 }
 
diff --git a/src/test/bench/shootout-threadring.rs b/src/test/bench/shootout-threadring.rs
index 213c5140ccf0c..9eb8a29cec030 100644
--- a/src/test/bench/shootout-threadring.rs
+++ b/src/test/bench/shootout-threadring.rs
@@ -10,8 +10,6 @@
 
 // Based on threadring.erlang by Jira Isa
 
-// xfail-test FIXME #5985 OOM's on the mac bot
-
 fn start(n_tasks: int, token: int) {
     let mut (p, ch1) = comm::stream();
     ch1.send(token);