diff --git a/configure/os/CONFIG.Common.win32-x86-cygwin b/configure/os/CONFIG.Common.win32-x86-cygwin
index 38bd1c0a6..9e61cf4a8 100644
--- a/configure/os/CONFIG.Common.win32-x86-cygwin
+++ b/configure/os/CONFIG.Common.win32-x86-cygwin
@@ -15,6 +15,8 @@ ARCH_CLASS = x86
 
 EXE=.exe
 
+COMPILER_CPPFLAGS = -D_REENTRANT
+
 #POSIX_CPPFLAGS_YES = -D_POSIX_SOURCE=199506L -D_POSIX_THREADS -D_POSIX_TIMERS
 # _POSIX_SOURCE eliminates select()
 POSIX_CPPFLAGS_YES = -D_POSIX_THREADS -D_POSIX_TIMERS