3 files changed, 29 insertions, 6 deletions

diff --git a/include/mruby.h b/include/mruby.h
index 925344502..fac7e6fcd 100644
--- a/include/mruby.h
+++ b/include/mruby.h
@@ -61,6 +61,13 @@ typedef struct {
   struct REnv *env;
 } mrb_callinfo;
 
+enum mrb_fiber_state {
+  MRB_FIBER_CREATED = 0,
+  MRB_FIBER_RUNNING,
+  MRB_FIBER_RESUMED,
+  MRB_FIBER_TERMINATED,
+};
+
 struct mrb_context {
   struct mrb_context *prev;
 
@@ -75,6 +82,7 @@ struct mrb_context {
   struct RProc **ensure;
   int esize;
 
+  uint8_t status;
   struct RFiber *fib;
 };
 
diff --git a/mrbgems/mruby-fiber/src/fiber.c b/mrbgems/mruby-fiber/src/fiber.c
index c338b8b95..c98dd0e67 100644
--- a/mrbgems/mruby-fiber/src/fiber.c
+++ b/mrbgems/mruby-fiber/src/fiber.c
@@ -105,6 +105,7 @@ fiber_init(mrb_state *mrb, mrb_value self)
   c->ci++;                      /* push dummy callinfo */
 
   c->fib = f;
+  c->status = MRB_FIBER_CREATED;
 
   return self;
 }
@@ -153,8 +154,15 @@ fiber_resume(mrb_state *mrb, mrb_value self)
   mrb_value *a;
   int len;
 
+  if (c->status == MRB_FIBER_RESUMED) {
+    mrb_raise(mrb, E_RUNTIME_ERROR, "double resume");
+  }
+  if (c->status == MRB_FIBER_TERMINATED) {
+    mrb_raise(mrb, E_RUNTIME_ERROR, "resuming dead fiber");
+  }
   mrb_get_args(mrb, "*", &a, &len);
-  if (!c->prev) {               /* first call */
+  mrb->c->status = MRB_FIBER_RESUMED;
+  if (c->status == MRB_FIBER_CREATED) {
     mrb_value *b = c->stack+1;
     mrb_value *e = b + len;
 
@@ -163,16 +171,15 @@ fiber_resume(mrb_state *mrb, mrb_value self)
     }
     c->ci->argc = len;
     c->prev = mrb->c;
+    c->status = MRB_FIBER_RUNNING;
     mrb->c = c;
 
     MARK_CONTEXT_MODIFY(c);
     return c->ci->proc->env->stack[0];
   }
-  if (c->ci == c->cibase) {
-    mrb_raise(mrb, E_RUNTIME_ERROR, "resuming dead fiber");
-  }
   MARK_CONTEXT_MODIFY(c);
   c->prev = mrb->c;
+  c->status = MRB_FIBER_RUNNING;
   mrb->c = c;
   return fiber_result(mrb, a, len);
 }
@@ -198,8 +205,9 @@ fiber_yield(mrb_state *mrb, mrb_value self)
     mrb_raise(mrb, E_ARGUMENT_ERROR, "can't yield from root fiber");
   }
   mrb_get_args(mrb, "*", &a, &len);
-
+  c->prev->status = MRB_FIBER_RUNNING;
   mrb->c = c->prev;
+  c->prev = NULL;
   MARK_CONTEXT_MODIFY(mrb->c);
   return fiber_result(mrb, a, len);
 }
diff --git a/src/vm.c b/src/vm.c
index c240ef968..f9aec1520 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -1301,7 +1301,14 @@ mrb_run(mrb_state *mrb, struct RProc *proc, mrb_value self)
               localjump_error(mrb, LOCALJUMP_ERROR_RETURN);
               goto L_RAISE;
             }
-            mrb->c = mrb->c->prev; /* automatic yield at the end */
+            if (mrb->c->prev->ci == mrb->c->prev->cibase) {
+              mrb_value exc = mrb_exc_new3(mrb, E_RUNTIME_ERROR, mrb_str_new(mrb, "double resume", 13));
+              mrb->exc = mrb_obj_ptr(exc);
+              goto L_RAISE;
+            }
+            /* automatic yield at the end */
+            mrb->c->status = MRB_FIBER_TERMINATED;
+            mrb->c = mrb->c->prev;
           }
           ci = mrb->c->ci;
           break;