diff --git a/core/exception/system_call_error_spec.rb b/core/exception/system_call_error_spec.rb
index 7235aa9c26..f6995d3c5e 100644
--- a/core/exception/system_call_error_spec.rb
+++ b/core/exception/system_call_error_spec.rb
@@ -96,11 +96,23 @@ def initialize
   end
 
   it "sets an 'unknown error' message when an unknown error number" do
-    SystemCallError.new(-1).message.should =~ /Unknown error(:)? -1/
+    platform_is_not :windows do
+      SystemCallError.new(-1).message.should =~ /Unknown error(:)? -1/
+    end
+
+    platform_is :windows do
+      SystemCallError.new(-1).message.should == "The operation completed successfully."
+    end
   end
 
   it "adds a custom error message to an 'unknown error' message when an unknown error number and a custom message specified" do
-    SystemCallError.new("custom message", -1).message.should =~ /Unknown error(:)? -1 - custom message/
+    platform_is_not :windows do
+      SystemCallError.new("custom message", -1).message.should =~ /Unknown error(:)? -1 - custom message/
+    end
+
+    platform_is :windows do
+      SystemCallError.new("custom message", -1).message.should == "The operation completed successfully. - custom message"
+    end
   end
 
   it "converts to Integer if errno is a Complex convertible to Integer" do
diff --git a/optional/capi/io_spec.rb b/optional/capi/io_spec.rb
index a34b3a4ff0..dbfaf556f6 100644
--- a/optional/capi/io_spec.rb
+++ b/optional/capi/io_spec.rb
@@ -531,123 +531,135 @@
       end
     end
 
-    describe "rb_io_open_descriptor" do
-      it "creates a new IO instance" do
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-        io.should.is_a?(IO)
-      end
+    quarantine! do # "Errno::EBADF: Bad file descriptor" at closing @r_io, @rw_io etc in the after :each hook
+      describe "rb_io_open_descriptor" do
+        it "creates a new IO instance" do
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+          io.should.is_a?(IO)
+        end
 
-      it "return an instance of the specified class" do
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-        io.class.should == File
+        it "return an instance of the specified class" do
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+          io.class.should == File
 
-        io = @o.rb_io_open_descriptor(IO, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-        io.class.should == IO
-      end
+          io = @o.rb_io_open_descriptor(IO, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+          io.class.should == IO
+        end
 
-      it "sets the specified file descriptor" do
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-        io.fileno.should == @r_io.fileno
-      end
+        it "sets the specified file descriptor" do
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+          io.fileno.should == @r_io.fileno
+        end
 
-      it "sets the specified path" do
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-        io.path.should == "a.txt"
-      end
+        it "sets the specified path" do
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+          io.path.should == "a.txt"
+        end
 
-      it "sets the specified mode" do
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, CApiIOSpecs::FMODE_BINMODE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-        io.should.binmode?
+        it "sets the specified mode" do
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, CApiIOSpecs::FMODE_BINMODE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+          io.should.binmode?
 
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, CApiIOSpecs::FMODE_TEXTMODE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-        io.should_not.binmode?
-      end
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, CApiIOSpecs::FMODE_TEXTMODE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+          io.should_not.binmode?
+        end
 
-      it "sets the specified timeout" do
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-        io.timeout.should == 60
-      end
+        it "sets the specified timeout" do
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+          io.timeout.should == 60
+        end
 
-      it "sets the specified internal encoding" do
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-        io.internal_encoding.should == Encoding::US_ASCII
-      end
+        it "sets the specified internal encoding" do
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+          io.internal_encoding.should == Encoding::US_ASCII
+        end
 
-      it "sets the specified external encoding" do
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-        io.external_encoding.should == Encoding::UTF_8
-      end
+        it "sets the specified external encoding" do
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+          io.external_encoding.should == Encoding::UTF_8
+        end
 
-      it "does not apply the specified encoding flags" do
-        File.write("a.txt", "123\r\n456\n89")
-        file = File.open("a.txt", "r")
+        it "does not apply the specified encoding flags" do
+          name = tmp("rb_io_open_descriptor_specs")
+          File.write(name, "123\r\n456\n89")
+          file = File.open(name, "r")
 
-        io = @o.rb_io_open_descriptor(File, file.fileno, CApiIOSpecs::FMODE_READABLE, "a.txt", 60, "US-ASCII", "UTF-8", CApiIOSpecs::ECONV_UNIVERSAL_NEWLINE_DECORATOR, {})
-        io.read_nonblock(20).should == "123\r\n456\n89"
-      end
+          io = @o.rb_io_open_descriptor(File, file.fileno, CApiIOSpecs::FMODE_READABLE, "a.txt", 60, "US-ASCII", "UTF-8", CApiIOSpecs::ECONV_UNIVERSAL_NEWLINE_DECORATOR, {})
+          io.read_nonblock(20).should == "123\r\n456\n89"
+        ensure
+          file.close
+          rm_r name
+        end
 
-      it "ignores the IO open options" do
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {external_encoding: "windows-1251"})
-        io.external_encoding.should == Encoding::UTF_8
+        it "ignores the IO open options" do
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {external_encoding: "windows-1251"})
+          io.external_encoding.should == Encoding::UTF_8
 
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {internal_encoding: "windows-1251"})
-        io.internal_encoding.should == Encoding::US_ASCII
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {internal_encoding: "windows-1251"})
+          io.internal_encoding.should == Encoding::US_ASCII
 
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {encoding: "windows-1251:binary"})
-        io.external_encoding.should == Encoding::UTF_8
-        io.internal_encoding.should == Encoding::US_ASCII
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {encoding: "windows-1251:binary"})
+          io.external_encoding.should == Encoding::UTF_8
+          io.internal_encoding.should == Encoding::US_ASCII
 
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {textmode: false})
-        io.should_not.binmode?
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {textmode: false})
+          io.should_not.binmode?
 
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {binmode: true})
-        io.should_not.binmode?
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {binmode: true})
+          io.should_not.binmode?
 
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {autoclose: false})
-        io.should.autoclose?
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {autoclose: false})
+          io.should.autoclose?
 
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {path: "a.txt"})
-        io.path.should == "a.txt"
-      end
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {path: "a.txt"})
+          io.path.should == "a.txt"
+        end
 
-      it "ignores the IO encoding options" do
-        io = @o.rb_io_open_descriptor(File, @w_io.fileno, CApiIOSpecs::FMODE_WRITABLE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {crlf_newline: true})
+        it "ignores the IO encoding options" do
+          io = @o.rb_io_open_descriptor(File, @w_io.fileno, CApiIOSpecs::FMODE_WRITABLE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {crlf_newline: true})
 
-        io.write("123\r\n456\n89")
-        io.flush
+          io.write("123\r\n456\n89")
+          io.flush
 
-        @r_io.read_nonblock(20).should == "123\r\n456\n89"
-      end
+          @r_io.read_nonblock(20).should == "123\r\n456\n89"
+        end
 
-      it "allows wrong mode" do
-        io = @o.rb_io_open_descriptor(File, @w_io.fileno, CApiIOSpecs::FMODE_READABLE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-        io.should.is_a?(File)
+        it "allows wrong mode" do
+          io = @o.rb_io_open_descriptor(File, @w_io.fileno, CApiIOSpecs::FMODE_READABLE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+          io.should.is_a?(File)
 
-        -> { io.read_nonblock(1) }.should raise_error(Errno::EBADF)
-      end
+          platform_is_not :windows do
+            -> { io.read_nonblock(1) }.should raise_error(Errno::EBADF)
+          end
 
-      it "tolerates NULL as rb_io_encoding *encoding parameter" do
-        io = @o.rb_io_open_descriptor_without_encoding(File, @r_io.fileno, 0, "a.txt", 60)
-        io.should.is_a?(File)
-      end
+          platform_is :windows do
+            -> { io.read_nonblock(1) }.should raise_error(IO::EWOULDBLOCKWaitReadable)
+          end
+        end
+
+        it "tolerates NULL as rb_io_encoding *encoding parameter" do
+          io = @o.rb_io_open_descriptor_without_encoding(File, @r_io.fileno, 0, "a.txt", 60)
+          io.should.is_a?(File)
+        end
 
-      it "deduplicates path String" do
-        path = "a.txt".dup
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, path, 60, "US-ASCII", "UTF-8", 0, {})
-        io.path.should_not equal(path)
+        it "deduplicates path String" do
+          path = "a.txt".dup
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, path, 60, "US-ASCII", "UTF-8", 0, {})
+          io.path.should_not equal(path)
 
-        path = "a.txt".freeze
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, path, 60, "US-ASCII", "UTF-8", 0, {})
-        io.path.should_not equal(path)
-      end
+          path = "a.txt".freeze
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, path, 60, "US-ASCII", "UTF-8", 0, {})
+          io.path.should_not equal(path)
+        end
 
-      it "calls #to_str to convert a path to a String" do
-        path = Object.new
-        def path.to_str; "a.txt"; end
+        it "calls #to_str to convert a path to a String" do
+          path = Object.new
+          def path.to_str; "a.txt"; end
 
-        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, path, 60, "US-ASCII", "UTF-8", 0, {})
+          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, path, 60, "US-ASCII", "UTF-8", 0, {})
 
-        io.path.should == "a.txt"
+          io.path.should == "a.txt"
+        end
       end
     end
   end
diff --git a/optional/capi/kernel_spec.rb b/optional/capi/kernel_spec.rb
index 96d61ee003..c90e50f1db 100644
--- a/optional/capi/kernel_spec.rb
+++ b/optional/capi/kernel_spec.rb
@@ -197,9 +197,13 @@ class CApiKernelSpecs::Exc < StandardError
     end
 
     it "uses an 'unknown error' message when errno is unknown" do
-      -> do
-        @s.rb_syserr_fail(-10, nil)
-      end.should raise_error(SystemCallError, /Unknown error(:)? -1/) # a new class Errno::E-01 is generated on the fly
+      platform_is_not :windows do
+        -> { @s.rb_syserr_fail(-10, nil) }.should raise_error(SystemCallError, /Unknown error(:)? -10/)
+      end
+
+      platform_is :windows do
+        -> { @s.rb_syserr_fail(-1, nil) }.should raise_error(SystemCallError, "The operation completed successfully.")
+      end
     end
   end
 
@@ -217,9 +221,13 @@ class CApiKernelSpecs::Exc < StandardError
     end
 
     it "uses an 'unknown error' message when errno is unknown" do
-      -> do
-        @s.rb_syserr_fail_str(-1, nil)
-      end.should raise_error(SystemCallError, /Unknown error(:)? -1/) # a new class Errno::E-01 is generated on the fly
+      platform_is_not :windows do
+        -> { @s.rb_syserr_fail_str(-10, nil) }.should raise_error(SystemCallError, /Unknown error(:)? -10/)
+      end
+
+      platform_is :windows do
+        -> { @s.rb_syserr_fail_str(-1, nil) }.should raise_error(SystemCallError, "The operation completed successfully.")
+      end
     end
   end