diff --git a/include/mruby.h b/include/mruby.h
index 7a533cfa7..3ed86f8c7 100644
--- a/include/mruby.h
+++ b/include/mruby.h
@@ -1458,8 +1458,6 @@ MRB_API mrb_value mrb_fiber_new(mrb_state *mrb, const struct RProc *proc);
  * Implemented in mruby-fiber
  *
  * Switches to the specified fiber and executes. Like the `Fiber#resume` method.
- *
- * @note It can only be called before entering the mruby VM (e.g. in the `main()` function).
  */
 MRB_API mrb_value mrb_fiber_resume(mrb_state *mrb, mrb_value fib, mrb_int argc, const mrb_value *argv);
 
diff --git a/mrbgems/mruby-fiber/src/fiber.c b/mrbgems/mruby-fiber/src/fiber.c
index e91415dfe..4deb0d6a4 100644
--- a/mrbgems/mruby-fiber/src/fiber.c
+++ b/mrbgems/mruby-fiber/src/fiber.c
@@ -170,6 +170,17 @@ fiber_check_cfunc(mrb_state *mrb, struct mrb_context *c)
   }
 }
 
+static void
+fiber_check_cfunc_recursive(mrb_state *mrb, struct mrb_context *c)
+{
+  for (;; c = c->prev) {
+    fiber_check_cfunc(mrb, c);
+    if (c == mrb->root_c || !c->prev) {
+      break;
+    }
+  }
+}
+
 static void
 fiber_switch_context(mrb_state *mrb, struct mrb_context *c)
 {
@@ -275,14 +286,17 @@ fiber_switch(mrb_state *mrb, mrb_value self, mrb_int len, const mrb_value *a, mr
   else {
     value = fiber_result(mrb, a, len);
     if (vmexec) {
+      if (c->ci > c->cibase) c->ci--; /* pop dummy callinfo */
       c->ci[1].stack[0] = value;
     }
   }
 
   if (vmexec) {
+    int cci = old_c->ci->cci;
     c->vmexec = TRUE;
     value = mrb_vm_exec(mrb, c->ci->proc, c->ci->pc);
     mrb->c = old_c;
+    old_c->ci->cci = cci; /* restore values as they may have changed in Fiber.yield */
   }
   else {
     MARK_CONTEXT_MODIFY(c);
@@ -304,19 +318,19 @@ fiber_switch(mrb_state *mrb, mrb_value self, mrb_int len, const mrb_value *a, mr
  *  to the next <code>Fiber.yield</code> statement inside the fiber's block
  *  or to the block value if it runs to completion without any
  *  <code>Fiber.yield</code>
- *
- *  This method cannot be called from C using <code>mrb_funcall()</code>.
- *  Use <code>mrb_fiber_resume()</code> function instead.
  */
 static mrb_value
 fiber_resume(mrb_state *mrb, mrb_value self)
 {
   const mrb_value *a;
   mrb_int len;
+  mrb_bool vmexec = FALSE;
 
-  fiber_check_cfunc(mrb, mrb->c);
   mrb_get_args(mrb, "*!", &a, &len);
-  return fiber_switch(mrb, self, len, a, TRUE, FALSE);
+  if (mrb->c->ci->cci > 0) {
+    vmexec = TRUE;
+  }
+  return fiber_switch(mrb, self, len, a, TRUE, vmexec);
 }
 
 MRB_API mrb_value
@@ -429,7 +443,7 @@ fiber_transfer(mrb_state *mrb, mrb_value self)
   const mrb_value* a;
   mrb_int len;
 
-  fiber_check_cfunc(mrb, mrb->c);
+  fiber_check_cfunc_recursive(mrb, mrb->c);
   mrb_get_args(mrb, "*!", &a, &len);
 
   if (c->status == MRB_FIBER_RESUMED) {
@@ -472,7 +486,6 @@ mrb_fiber_yield(mrb_state *mrb, mrb_int len, const mrb_value *a)
   if (c->vmexec) {
     c->vmexec = FALSE;
     mrb->c->ci->cci = CINFO_RESUMED;
-    c->ci--;                    /* pop callinfo for yield */
   }
   MARK_CONTEXT_MODIFY(mrb->c);
   return fiber_result(mrb, a, len);
diff --git a/mrbgems/mruby-fiber/test/fiber.rb b/mrbgems/mruby-fiber/test/fiber.rb
index 64b9d8175..ea541acf3 100644
--- a/mrbgems/mruby-fiber/test/fiber.rb
+++ b/mrbgems/mruby-fiber/test/fiber.rb
@@ -1,204 +1,210 @@
-assert('Fiber.new') do
-  f = Fiber.new{}
-  assert_kind_of Fiber, f
-end
+begin
+  $fiber_test_activity = __FILE__
 
-assert('Fiber#resume') do
-  f = Fiber.new{|x| x }
-  assert_equal 2, f.resume(2)
-end
-
-assert('Fiber#transfer') do
-  ary = []
-  f2 = nil
-  f1 = Fiber.new{
-    ary << f2.transfer(:foo)
-    :ok
-  }
-  f2 = Fiber.new{
-    ary << f1.transfer(:baz)
-    :ng
-  }
-  assert_equal(:ok, f1.transfer)
-  assert_equal([:baz], ary)
-  assert_false f1.alive?
-end
-
-assert('Fiber#alive?') do
-  f = Fiber.new{ Fiber.yield }
-  f.resume
-  assert_true f.alive?
-  f.resume
-  assert_false f.alive?
-end
-
-assert('Fiber#==') do
-  root = Fiber.current
-  assert_equal root, root
-  assert_equal root, Fiber.current
-  assert_false root != Fiber.current
-  f = Fiber.new {
-    assert_false root == Fiber.current
-  }
-  f.resume
-  assert_false f == root
-  assert_true f != root
-end
-
-assert('Fiber.yield') do
-  f = Fiber.new{|x| Fiber.yield x }
-  assert_equal 3, f.resume(3)
-  assert_true f.alive?
-end
-
-assert('FiberError') do
-  assert_equal StandardError, FiberError.superclass
-end
-
-assert('Fiber iteration') do
-  f1 = Fiber.new{
-    [1,2,3].each{|x| Fiber.yield(x)}
-  }
-  f2 = Fiber.new{
-    [9,8,7].each{|x| Fiber.yield(x)}
-  }
-  a = []
-  3.times {
-    a << f1.resume
-    a << f2.resume
-  }
-  assert_equal [1,9,2,8,3,7], a
-end
-
-assert('Fiber with splat in the block argument list') {
-  assert_equal([1], Fiber.new{|*x|x}.resume(1))
-}
-
-assert('Fiber raises on resume when dead') do
-  assert_raise(FiberError) do
+  assert('Fiber.new') do
     f = Fiber.new{}
+    assert_kind_of Fiber, f
+  end
+
+  assert('Fiber#resume') do
+    f = Fiber.new{|x| x }
+    assert_equal 2, f.resume(2)
+  end
+
+  assert('Fiber#transfer') do
+    ary = []
+    f2 = nil
+    f1 = Fiber.new{
+      ary << f2.transfer(:foo)
+      :ok
+    }
+    f2 = Fiber.new{
+      ary << f1.transfer(:baz)
+      :ng
+    }
+    assert_equal(:ok, f1.transfer)
+    assert_equal([:baz], ary)
+    assert_false f1.alive?
+  end
+
+  assert('Fiber#alive?') do
+    f = Fiber.new{ Fiber.yield }
+    f.resume
+    assert_true f.alive?
     f.resume
     assert_false f.alive?
-    f.resume
   end
-end
 
-assert('Yield raises when called on root fiber') do
-  assert_raise(FiberError) { Fiber.yield }
-end
+  assert('Fiber#==') do
+    root = Fiber.current
+    assert_equal root, root
+    assert_equal root, Fiber.current
+    assert_false root != Fiber.current
+    f = Fiber.new {
+      assert_false root == Fiber.current
+    }
+    f.resume
+    assert_false f == root
+    assert_true f != root
+  end
 
-assert('Double resume of Fiber') do
-  f1 = Fiber.new {}
-  f2 = Fiber.new {
-    f1.resume
-    assert_raise(FiberError) { f2.resume }
-    Fiber.yield 0
+  assert('Fiber.yield') do
+    f = Fiber.new{|x| Fiber.yield x }
+    assert_equal 3, f.resume(3)
+    assert_true f.alive?
+  end
+
+  assert('FiberError') do
+    assert_equal StandardError, FiberError.superclass
+  end
+
+  assert('Fiber iteration') do
+    f1 = Fiber.new{
+      [1,2,3].each{|x| Fiber.yield(x)}
+    }
+    f2 = Fiber.new{
+      [9,8,7].each{|x| Fiber.yield(x)}
+    }
+    a = []
+    3.times {
+      a << f1.resume
+      a << f2.resume
+    }
+    assert_equal [1,9,2,8,3,7], a
+  end
+
+  assert('Fiber with splat in the block argument list') {
+    assert_equal([1], Fiber.new{|*x|x}.resume(1))
   }
-  assert_equal 0, f2.resume
-  f2.resume
-  assert_false f1.alive?
-  assert_false f2.alive?
-end
 
-assert('Recursive resume of Fiber') do
-  f1, f2 = nil, nil
-  f1 = Fiber.new { assert_raise(FiberError) { f2.resume } }
-  f2 = Fiber.new {
-    f1.resume
-    Fiber.yield 0
-  }
-  f3 = Fiber.new {
+  assert('Fiber raises on resume when dead') do
+    assert_raise(FiberError) do
+      f = Fiber.new{}
+      f.resume
+      assert_false f.alive?
+      f.resume
+    end
+  end
+
+  assert('Yield raises when called on root fiber') do
+    assert_raise(FiberError) { Fiber.yield }
+  end
+
+  assert('Double resume of Fiber') do
+    f1 = Fiber.new {}
+    f2 = Fiber.new {
+      f1.resume
+      assert_raise(FiberError) { f2.resume }
+      Fiber.yield 0
+    }
+    assert_equal 0, f2.resume
     f2.resume
-  }
-  assert_equal 0, f3.resume
-  f2.resume
-  assert_false f1.alive?
-  assert_false f2.alive?
-  assert_false f3.alive?
-end
+    assert_false f1.alive?
+    assert_false f2.alive?
+  end
 
-assert('Root fiber resume') do
-  root = Fiber.current
-  assert_raise(FiberError) { root.resume }
-  f = Fiber.new {
+  assert('Recursive resume of Fiber') do
+    f1, f2 = nil, nil
+    f1 = Fiber.new { assert_raise(FiberError) { f2.resume } }
+    f2 = Fiber.new {
+      f1.resume
+      Fiber.yield 0
+    }
+    f3 = Fiber.new {
+      f2.resume
+    }
+    assert_equal 0, f3.resume
+    f2.resume
+    assert_false f1.alive?
+    assert_false f2.alive?
+    assert_false f3.alive?
+  end
+
+  assert('Root fiber resume') do
+    root = Fiber.current
     assert_raise(FiberError) { root.resume }
-  }
-  f.resume
-  assert_false f.alive?
-end
-
-assert('Fiber without block') do
-  assert_raise(ArgumentError) { Fiber.new }
-end
-
-
-assert('Transfer to self.') do
-  result = []
-  f = Fiber.new { result << :start; f.transfer; result << :end }
-  f.transfer
-  assert_equal [:start, :end], result
-
-  result = []
-  f = Fiber.new { result << :start; f.transfer; result << :end }
-  f.resume
-  assert_equal [:start, :end], result
-end
-
-assert('Resume transferred fiber') do
-  f = Fiber.new {
-    assert_raise(FiberError) { f.resume }
-  }
-  f.transfer
-end
-
-assert('Root fiber transfer.') do
-  result = nil
-  root = Fiber.current
-  f = Fiber.new {
-    result = :ok
-    root.transfer
-  }
-  f.transfer
-  assert_true f.alive?
-  assert_equal :ok, result
-end
-
-assert('Break nested fiber with root fiber transfer') do
-  root = Fiber.current
-
-  result = nil
-  f2 = nil
-  f1 = Fiber.new {
-    root.transfer(f2.transfer)
-    result = :f1
-  }
-  f2 = Fiber.new {
-    result = :to_root
-    root.transfer :from_f2
-    result = :f2
-  }
-  assert_equal :from_f2, f1.transfer
-  assert_equal :to_root, result
-  assert_equal :f2, f2.transfer
-  assert_equal :f2, result
-  assert_false f2.alive?
-  assert_equal nil, f1.transfer
-  assert_equal :f1, f1.transfer
-  assert_equal :f1, result
-  assert_false f1.alive?
-end
-
-assert('CRuby Fiber#transfer test.') do
-  ary = []
-  f2 = nil
-  f1 = Fiber.new{
-    ary << f2.transfer(:foo)
-    :ok
-  }
-  f2 = Fiber.new{
-    ary << f1.transfer(:baz)
-    :ng
-  }
-  assert_equal :ok, f1.transfer
-  assert_equal [:baz], ary
+    f = Fiber.new {
+      assert_raise(FiberError) { root.resume }
+    }
+    f.resume
+    assert_false f.alive?
+  end
+
+  assert('Fiber without block') do
+    assert_raise(ArgumentError) { Fiber.new }
+  end
+
+
+  assert('Transfer to self.') do
+    result = []
+    f = Fiber.new { result << :start; f.transfer; result << :end }
+    f.transfer
+    assert_equal [:start, :end], result
+
+    result = []
+    f = Fiber.new { result << :start; f.transfer; result << :end }
+    f.resume
+    assert_equal [:start, :end], result
+  end
+
+  assert('Resume transferred fiber') do
+    f = Fiber.new {
+      assert_raise(FiberError) { f.resume }
+    }
+    f.transfer
+  end
+
+  assert('Root fiber transfer.') do
+    result = nil
+    root = Fiber.current
+    f = Fiber.new {
+      result = :ok
+      root.transfer
+    }
+    f.transfer
+    assert_true f.alive?
+    assert_equal :ok, result
+  end
+
+  assert('Break nested fiber with root fiber transfer') do
+    root = Fiber.current
+
+    result = nil
+    f2 = nil
+    f1 = Fiber.new {
+      root.transfer(f2.transfer)
+      result = :f1
+    }
+    f2 = Fiber.new {
+      result = :to_root
+      root.transfer :from_f2
+      result = :f2
+    }
+    assert_equal :from_f2, f1.transfer
+    assert_equal :to_root, result
+    assert_equal :f2, f2.transfer
+    assert_equal :f2, result
+    assert_false f2.alive?
+    assert_equal nil, f1.transfer
+    assert_equal :f1, f1.transfer
+    assert_equal :f1, result
+    assert_false f1.alive?
+  end
+
+  assert('CRuby Fiber#transfer test.') do
+    ary = []
+    f2 = nil
+    f1 = Fiber.new{
+      ary << f2.transfer(:foo)
+      :ok
+    }
+    f2 = Fiber.new{
+      ary << f1.transfer(:baz)
+      :ng
+    }
+    assert_equal :ok, f1.transfer
+    assert_equal [:baz], ary
+  end
+ensure
+  $fiber_test_activity = nil
 end
diff --git a/mrbgems/mruby-fiber/test/fiber2.rb b/mrbgems/mruby-fiber/test/fiber2.rb
new file mode 100644
index 000000000..a6ff8a791
--- /dev/null
+++ b/mrbgems/mruby-fiber/test/fiber2.rb
@@ -0,0 +1,155 @@
+# This file tests fiber switching crossing C functions
+
+unless RUBY_ENGINE == "mruby"
+  class Fiber
+    alias resume_by_c_func resume
+    alias resume_by_c_method resume
+
+    class << self
+      alias yield_by_c_func yield
+
+      def yield_by_c_method(*args)
+        raise FiberError, "ycan't cross C function boundary"
+      end
+    end
+  end
+
+  def Proc.c_tunnel
+    yield
+  end
+end
+
+begin
+  $fiber_test_activity = __FILE__
+
+  assert('Call Fiber#resume nested with C') do
+    assert_equal "ok1", Fiber.new { Fiber.new { "ok1" }.resume_by_c_func }.resume_by_c_func
+    assert_equal "ok2", Fiber.new { Fiber.new { "ok2" }.resume_by_c_method }.resume_by_c_func
+    assert_equal "ok3", Fiber.new { Fiber.new { "ok3" }.resume_by_c_func }.resume_by_c_method
+    assert_equal "ok4", Fiber.new { Fiber.new { "ok4" }.resume_by_c_method }.resume_by_c_method
+    assert_equal "ok5", Fiber.new { Proc.c_tunnel { Fiber.new { "ok5" }.resume_by_c_func } }.resume_by_c_func
+    assert_equal "ok6", Fiber.new { Proc.c_tunnel { Fiber.new { "ok6" }.resume_by_c_method } }.resume_by_c_func
+    assert_equal "ok7", Fiber.new { Proc.c_tunnel { Fiber.new { "ok7" }.resume_by_c_func } }.resume_by_c_method
+    assert_equal "ok8", Fiber.new { Proc.c_tunnel { Fiber.new { "ok8" }.resume_by_c_method } }.resume_by_c_method
+    assert_equal "ok9", Fiber.new { Proc.c_tunnel { Fiber.new { "ok9" }.resume } }.resume_by_c_func
+    assert_equal "ok10", Fiber.new { Proc.c_tunnel { Fiber.new { "ok10" }.resume } }.resume_by_c_method
+  end
+
+  assert('Call Fiber#resume and Fiber.yield mixed with C.') do
+    assert_equal 1, Fiber.new { Fiber.yield 1 }.resume_by_c_func
+    assert_equal 2, Fiber.new { Fiber.yield 2 }.resume_by_c_method
+    assert_equal 3, Fiber.new { Fiber.yield_by_c_func 3 }.resume
+    assert_equal 4, Fiber.new { Fiber.yield_by_c_func 4 }.resume_by_c_func
+    assert_equal 5, Fiber.new { Fiber.yield_by_c_func 5 }.resume_by_c_method
+    assert_raise(FiberError) { Fiber.new { Fiber.yield_by_c_method "bad" }.resume }
+    assert_raise(FiberError) { Fiber.new { Fiber.yield_by_c_method "bad" }.resume_by_c_func }
+    assert_raise(FiberError) { Fiber.new { Fiber.yield_by_c_method "bad" }.resume_by_c_method }
+
+    result = []
+    f1 = Fiber.new { result << Fiber.new { Fiber.yield 1; "bad" }.resume_by_c_func; 2 }
+    f2 = Fiber.new { result << f1.resume; 3 }
+    result << f2.resume
+    assert_equal [1, 2, 3], result
+
+    f1 = Fiber.new {
+      -> {
+        Fiber.yield 1
+        Fiber.yield_by_c_func 2
+        f2 = Fiber.new {
+          -> {
+            Fiber.yield_by_c_func 3
+            Fiber.yield 4
+            Fiber.yield_by_c_func 5
+            Fiber.yield 6
+          }.call
+          7
+        }
+        Fiber.yield f2.resume_by_c_func
+        Fiber.yield f2.resume
+        Fiber.yield f2.resume_by_c_method
+        Fiber.yield f2.resume
+        Fiber.yield f2.resume_by_c_func
+        Fiber.yield 8
+      }.call
+      Fiber.yield 9
+      10
+    }
+    result = []
+    10.times { result << f1.resume }
+    assert_equal [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], result
+  end
+
+  assert('Call Fiber#resume and Fiber.yield mixed with C and raising exceptions') do
+    f = Fiber.new do
+      raise ZeroDivisionError
+    rescue
+      Fiber.yield "rescue"
+      "pass1"
+    ensure
+      Fiber.yield "ensure"
+    end
+    assert_equal "rescue", f.resume_by_c_method
+    assert_equal "ensure", f.resume_by_c_method
+    assert_equal "pass1", f.resume_by_c_method
+    assert_raise(FiberError) { f.resume_by_c_method }
+
+    f = Fiber.new do
+      raise ZeroDivisionError
+    rescue
+      Fiber.yield "rescue"
+      "pass2"
+    ensure
+      Fiber.yield "ensure"
+    end
+    assert_equal "rescue", f.resume_by_c_func
+    assert_equal "ensure", f.resume_by_c_func
+    assert_equal "pass2", f.resume_by_c_func
+    assert_raise(FiberError) { f.resume_by_c_func }
+
+    f2 = Fiber.new do
+      -> do
+        Fiber.yield 1
+        raise "3"
+      ensure
+        Fiber.yield 2
+      end.call
+      "NOT REACH 1"
+    end
+    f1 = Fiber.new do
+      Fiber.yield f2.resume_by_c_func
+      begin
+        Fiber.yield f2.resume
+        Fiber.yield f2.resume_by_c_method
+        Fiber.yield "NOT REACH 2"
+      rescue => e
+        Fiber.yield e.message
+        Fiber.yield 4
+      ensure
+        Fiber.yield 5
+      end
+      Fiber.yield 6
+      7
+    end
+    result = []
+    7.times { result << f1.resume }
+    assert_equal [1, 2, "3", 4, 5, 6, 7], result
+  end
+
+  assert('Call Fiber#transfer with C') do
+    assert_equal "ok1", Fiber.new { Fiber.new { "ok1" }.resume_by_c_method }.transfer
+    assert_equal "ok2", Fiber.new { Fiber.new { "ok2" }.resume_by_c_func }.transfer
+    assert_raise(FiberError) { Proc.c_tunnel { Fiber.new { "BAD!" }.transfer } }
+
+    b = Fiber.current
+    a = Fiber.new {
+      Proc.c_tunnel {
+        Fiber.new {
+          b.transfer
+        }.resume
+      }
+    }
+    assert_raise(FiberError) { a.transfer }
+  end
+ensure
+  $fiber_test_activity = nil
+end
diff --git a/mrbgems/mruby-fiber/test/fibertest.c b/mrbgems/mruby-fiber/test/fibertest.c
new file mode 100644
index 000000000..69680aecb
--- /dev/null
+++ b/mrbgems/mruby-fiber/test/fibertest.c
@@ -0,0 +1,87 @@
+#include <mruby.h>
+#include <mruby/string.h>
+#include <mruby/variable.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static mrb_value
+fiber_s_yield_by_c_func(mrb_state *mrb, mrb_value self)
+{
+  mrb_value a = mrb_get_arg1(mrb);
+  return mrb_fiber_yield(mrb, 1, &a);
+}
+
+static mrb_value
+fiber_s_yield_by_c_method(mrb_state *mrb, mrb_value self)
+{
+  mrb_value a = mrb_get_arg1(mrb);
+  return mrb_funcall_argv(mrb, self, mrb_intern_lit(mrb, "yield"), 1, &a);
+}
+
+static mrb_value
+fiber_resume_by_c_func(mrb_state *mrb, mrb_value self)
+{
+  int ci_index = mrb->c->ci - mrb->c->cibase;
+  mrb_value ret = mrb_fiber_resume(mrb, self, 0, NULL);
+  if (ci_index != mrb->c->ci - mrb->c->cibase) {
+    mrb_raisef(mrb, E_EXCEPTION,
+               "[BUG] INVALID CI POSITION (expected %d, but actual %d) [BUG]",
+               (int)ci_index, (int)(mrb->c->ci - mrb->c->cibase));
+  }
+  return ret;
+}
+
+static mrb_value
+fiber_resume_by_c_method(mrb_state *mrb, mrb_value self)
+{
+  int ci_index = mrb->c->ci - mrb->c->cibase;
+  mrb_value ret = mrb_funcall_argv(mrb, self, mrb_intern_lit(mrb, "resume"), 0, NULL);
+  if (ci_index != mrb->c->ci - mrb->c->cibase) {
+    mrb_raisef(mrb, E_EXCEPTION,
+               "[BUG] INVALID CI POSITION (expected %d, but actual %d) [BUG]",
+               (int)ci_index, (int)(mrb->c->ci - mrb->c->cibase));
+  }
+  return ret;
+}
+
+static mrb_value
+fiber_transfer_by_c(mrb_state *mrb, mrb_value self)
+{
+  return mrb_funcall_argv(mrb, self, mrb_intern_lit(mrb, "transfer"), 0, NULL);
+}
+
+static mrb_value
+proc_s_c_tunnel(mrb_state *mrb, mrb_value self)
+{
+  mrb_value b;
+  mrb_get_args(mrb, "&!", &b);
+  return mrb_yield_argv(mrb, b, 0, NULL);
+}
+
+static void
+check_activity(mrb_state *mrb)
+{
+  mrb_value act = mrb_gv_get(mrb, mrb_intern_lit(mrb, "$fiber_test_activity"));
+  if (mrb_test(act)) {
+    act = mrb_obj_as_string(mrb, act);
+    fprintf(stderr, "\n\t<<<%s%.*s>>>\n",
+            "mruby VM has an unexpected outage in ", (int)RSTRING_LEN(act), RSTRING_PTR(act));
+    abort();
+  }
+}
+
+void
+mrb_mruby_fiber_gem_test(mrb_state *mrb)
+{
+  struct RClass *fiber_class = mrb_class_get(mrb, "Fiber");
+  mrb_define_class_method(mrb, fiber_class, "yield_by_c_func", fiber_s_yield_by_c_func, MRB_ARGS_ANY());
+  mrb_define_class_method(mrb, fiber_class, "yield_by_c_method", fiber_s_yield_by_c_method, MRB_ARGS_ANY());
+  mrb_define_method(mrb, fiber_class, "resume_by_c_func", fiber_resume_by_c_func, MRB_ARGS_NONE());
+  mrb_define_method(mrb, fiber_class, "resume_by_c_method", fiber_resume_by_c_method, MRB_ARGS_NONE());
+  mrb_define_method(mrb, fiber_class, "transfer_by_c", fiber_transfer_by_c, MRB_ARGS_NONE());
+
+  mrb_define_class_method(mrb, mrb->proc_class, "c_tunnel", proc_s_c_tunnel, MRB_ARGS_NONE() | MRB_ARGS_BLOCK());
+
+  mrb_gv_set(mrb, mrb_intern_lit(mrb, "$fiber_test_activity"), mrb_nil_value());
+  mrb_state_atexit(mrb, check_activity);
+}
diff --git a/src/vm.c b/src/vm.c
index 2d2a919c4..35e1650f9 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -1839,6 +1839,7 @@ RETRY_TRY_BLOCK:
           }
           recv = MRB_METHOD_FUNC(m)(mrb, recv);
         }
+        mrb_assert(mrb->c->ci > mrb->c->cibase);
         mrb_gc_arena_shrink(mrb, ai);
         if (mrb->exc) goto L_RAISE;
         ci = mrb->c->ci;
@@ -2245,7 +2246,10 @@ RETRY_TRY_BLOCK:
             mrb->c = c->prev;
             if (!mrb->c) mrb->c = mrb->root_c;
             else c->prev = NULL;
-            goto L_RAISE;
+            if (!c->vmexec) goto L_RAISE;
+            mrb->jmp = prev_jmp;
+            if (!prev_jmp) return mrb_obj_value(mrb->exc);
+            MRB_THROW(prev_jmp);
           }
         }