diff --git a/test-environ.c b/test-environ.c
index 46a2eab..8afecb7 100644
--- a/test-environ.c
+++ b/test-environ.c
@@ -22,6 +22,13 @@
 
 #include <string.h>
 
+/* environ is the exported symbol referencing the internal
+   __cygwin_environ variable on cygwin64:
+   <https://cygwin.com/ml/cygwin/2013-06/msg00228.html>.  */
+#if defined __CYGWIN__ && defined __x86_64__
+extern DLL_VARIABLE char **environ;
+#endif
+
 int
 main ()
 {