diff --git a/src/include/cppduals/duals/dual b/src/include/cppduals/duals/dual
index 94688d185..4cb227e84 100644
--- a/src/include/cppduals/duals/dual
+++ b/src/include/cppduals/duals/dual
@@ -44,9 +44,11 @@ _LIBCPP_END_NAMESPACE_STD
 /// Configure whether system has POSIX extern int signgam;
 #ifndef CPPDUALS_HAVE_SIGNGAM
 #ifndef _WIN32
+#ifndef __CYGWIN__
 #define CPPDUALS_HAVE_SIGNGAM 1
 #endif
 #endif
+#endif
 namespace duals {
 
 /**