diff --git a/COPYING.BSD2 b/COPYING.BSD2
new file mode 100644
index 00000000..83f87e4d
--- /dev/null
+++ b/COPYING.BSD2
@@ -0,0 +1,20 @@
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+1. Redistributions of source code must retain the above copyright
+  notice, this list of conditions and the following disclaimer.
+2. Redistributions in binary form must reproduce the above copyright
+  notice, this list of conditions and the following disclaimer in the
+   documentation and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
diff --git a/README.md b/README.md
index bce54e61..12a2cf24 100644
--- a/README.md
+++ b/README.md
@@ -286,3 +286,7 @@ which has been made available for use in Open Source applications per the
 [license statement](COPYING.IEEE) on http://www.realitypixels.com/turk/opensource/.
 The only modification made to the code is to comment out the `TEST_FP` define
 to make it useable in the eSpeak NG library.
+
+The `getopt.c` compatibility implementation for getopt support on Windows is
+taken from the NetBSD `getopt_long` implementation, which is licensed under a
+[2-clause BSD](COPYING.BSD2) license.