diff --git a/ChangeLog b/ChangeLog
index 3a24bf8..5da4cd6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -67,6 +67,9 @@ EOF. The test looks to have come from a fuzzer.
 default default of 10 000 000, some JIT tests of the match limit no longer
 failed. All such tests now set 10 000 000 as the upper limit.
 
+16. Another Windows related patch for pcregrep to ensure that WIN32 is 
+undefiined under Cygwin.
+
 
 Version 10.31 12-February-2018
 ------------------------------
diff --git a/src/pcre2grep.c b/src/pcre2grep.c
index c7e63d7..f18693a 100644
--- a/src/pcre2grep.c
+++ b/src/pcre2grep.c
@@ -64,8 +64,8 @@ POSSIBILITY OF SUCH DAMAGE.
 #endif
 
 /* Some cmake's define it still */
-#if defined(__CYGWIN__) && !defined(WIN32)
-#define WIN32
+#if defined(__CYGWIN__) && defined(WIN32)
+#undef WIN32
 #endif
 
 #ifdef WIN32