diff --git a/core/io/pwrite_spec.rb b/core/io/pwrite_spec.rb
index c10578a8e..2691d2c11 100644
--- a/core/io/pwrite_spec.rb
+++ b/core/io/pwrite_spec.rb
@@ -28,6 +28,20 @@
       @file.pread(6, 0).should == "foobar"
     end
 
+    it "calls #to_s on the object to be written" do
+      data = mock("to_s")
+      data.should_receive(:to_s).and_return("foo")
+      @file.pwrite(data, 0)
+      @file.pread(3, 0).should == "foo"
+    end
+
+    it "calls #to_int on the offset" do
+      offset = mock("to_int")
+      offset.should_receive(:to_int).and_return(2)
+      @file.pwrite("foo", offset)
+      @file.pread(3, 2).should == "foo"
+    end
+
     it "raises IOError when file is not open in write mode" do
       File.open(@fname, "r") do |file|
         -> { file.pwrite("foo", 1) }.should raise_error(IOError)
@@ -39,5 +53,17 @@
       file.close
       -> { file.pwrite("foo", 1) }.should raise_error(IOError)
     end
+
+    it "raises a NoMethodError if #to_s cannot be called on the object to be written" do
+      -> {
+        @file.pwrite(BasicObject.new, 0)
+      }.should raise_error(NoMethodError, /undefined method `to_s'/)
+    end
+
+    it "raises a TypeError if the offset cannot be converted to an Integer" do
+      -> {
+        @file.pwrite("foo", Object.new)
+      }.should raise_error(TypeError, "no implicit conversion of Object into Integer")
+    end
   end
 end