diff --git a/library/io-wait/wait_readable_spec.rb b/library/io-wait/wait_readable_spec.rb
index d7473f029..ae433cdb0 100644
--- a/library/io-wait/wait_readable_spec.rb
+++ b/library/io-wait/wait_readable_spec.rb
@@ -1,4 +1,5 @@
 require_relative '../../spec_helper'
+require_relative '../../core/fiber/fixtures/scheduler'
 
 describe "IO#wait_readable" do
   before :each do
@@ -39,4 +40,45 @@
     rd.close
     wr.close
   end
+
+  context "with a Fiber scheduler" do
+    before :each do
+      @read, @write = IO.pipe
+      Fiber.set_scheduler(FiberSpecs::LoggingScheduler.new)
+    end
+
+    # An IO cannot be closed while a fiber is waiting on it, and the scheduler
+    # leaves the fiber parked inside #io_wait, so run it out before closing.
+    after :each do
+      @fiber.resume while @fiber&.alive?
+      Fiber.set_scheduler(nil)
+      @read.close unless @read.closed?
+      @write.close unless @write.closed?
+    end
+
+    it "calls the scheduler's #io_wait with IO::READABLE and no timeout" do
+      @fiber = Fiber.new(blocking: false) { @read.wait_readable }
+      @fiber.resume
+
+      Fiber.scheduler.events.should == [
+        { event: :io_wait, fiber: @fiber, args: [@read, IO::READABLE, nil] }
+      ]
+    end
+
+    it "passes the given timeout to the scheduler" do
+      @fiber = Fiber.new(blocking: false) { @read.wait_readable(1) }
+      @fiber.resume
+
+      Fiber.scheduler.events.should == [
+        { event: :io_wait, fiber: @fiber, args: [@read, IO::READABLE, 1] }
+      ]
+    end
+
+    it "does not call the scheduler if the fiber is blocking" do
+      @fiber = Fiber.new(blocking: true) { @read.wait_readable(0) }
+      @fiber.resume
+
+      Fiber.scheduler.events.should == []
+    end
+  end
 end
diff --git a/library/io-wait/wait_spec.rb b/library/io-wait/wait_spec.rb
index 1d784e7aa..e0f295c77 100644
--- a/library/io-wait/wait_spec.rb
+++ b/library/io-wait/wait_spec.rb
@@ -1,5 +1,6 @@
 require_relative '../../spec_helper'
 require_relative '../../fixtures/io'
+require_relative '../../core/fiber/fixtures/scheduler'
 
 describe "IO#wait" do
   before :each do
@@ -159,4 +160,52 @@
       -> { @io.wait(0, :r) }.should.raise(IOError, "closed stream")
     end
   end
+
+  context "with a Fiber scheduler" do
+    before :each do
+      Fiber.set_scheduler(FiberSpecs::LoggingScheduler.new)
+    end
+
+    # An IO cannot be closed while a fiber is waiting on it, and the scheduler
+    # leaves the fiber parked inside #io_wait, so run it out before the outer
+    # after hook closes the pipe.
+    after :each do
+      @fiber.resume while @fiber&.alive?
+      Fiber.set_scheduler(nil)
+    end
+
+    it "calls the scheduler's #io_wait with the events and timeout given" do
+      @fiber = Fiber.new(blocking: false) { @r.wait(IO::READABLE, 2) }
+      @fiber.resume
+
+      Fiber.scheduler.events.should == [
+        { event: :io_wait, fiber: @fiber, args: [@r, IO::READABLE, 2] }
+      ]
+    end
+
+    it "calls the scheduler's #io_wait with IO::READABLE when no events are given" do
+      @fiber = Fiber.new(blocking: false) { @r.wait }
+      @fiber.resume
+
+      Fiber.scheduler.events.should == [
+        { event: :io_wait, fiber: @fiber, args: [@r, IO::READABLE, nil] }
+      ]
+    end
+
+    it "translates a mode Symbol into the matching events mask" do
+      @fiber = Fiber.new(blocking: false) { @r.wait(0.5, :readable_writable) }
+      @fiber.resume
+
+      Fiber.scheduler.events.should == [
+        { event: :io_wait, fiber: @fiber, args: [@r, IO::READABLE | IO::WRITABLE, 0.5] }
+      ]
+    end
+
+    it "does not call the scheduler if the fiber is blocking" do
+      @fiber = Fiber.new(blocking: true) { @r.wait(IO::READABLE, 0) }
+      @fiber.resume
+
+      Fiber.scheduler.events.should == []
+    end
+  end
 end
diff --git a/library/io-wait/wait_writable_spec.rb b/library/io-wait/wait_writable_spec.rb
index 2017817ca..6959b48e4 100644
--- a/library/io-wait/wait_writable_spec.rb
+++ b/library/io-wait/wait_writable_spec.rb
@@ -1,5 +1,6 @@
 require_relative '../../spec_helper'
 require_relative '../../fixtures/io'
+require_relative '../../core/fiber/fixtures/scheduler'
 
 describe "IO#wait_writable" do
   it "waits for the IO to become writable with no timeout" do
@@ -34,4 +35,45 @@
     rd.close unless rd.closed?
     wr.close unless wr.closed?
   end
+
+  context "with a Fiber scheduler" do
+    before :each do
+      @read, @write = IO.pipe
+      Fiber.set_scheduler(FiberSpecs::LoggingScheduler.new)
+    end
+
+    # An IO cannot be closed while a fiber is waiting on it, and the scheduler
+    # leaves the fiber parked inside #io_wait, so run it out before closing.
+    after :each do
+      @fiber.resume while @fiber&.alive?
+      Fiber.set_scheduler(nil)
+      @read.close unless @read.closed?
+      @write.close unless @write.closed?
+    end
+
+    it "calls the scheduler's #io_wait with IO::WRITABLE and no timeout" do
+      @fiber = Fiber.new(blocking: false) { @write.wait_writable }
+      @fiber.resume
+
+      Fiber.scheduler.events.should == [
+        { event: :io_wait, fiber: @fiber, args: [@write, IO::WRITABLE, nil] }
+      ]
+    end
+
+    it "passes the given timeout to the scheduler" do
+      @fiber = Fiber.new(blocking: false) { @write.wait_writable(1) }
+      @fiber.resume
+
+      Fiber.scheduler.events.should == [
+        { event: :io_wait, fiber: @fiber, args: [@write, IO::WRITABLE, 1] }
+      ]
+    end
+
+    it "does not call the scheduler if the fiber is blocking" do
+      @fiber = Fiber.new(blocking: true) { @write.wait_writable(0) }
+      @fiber.resume
+
+      Fiber.scheduler.events.should == []
+    end
+  end
 end