diff --git a/Include/Python.h b/Include/Python.h
index 0511373..54ea321 100644
--- a/Include/Python.h
+++ b/Include/Python.h
@@ -36,7 +36,17 @@
 #include <unistd.h>
 #endif
 #ifdef HAVE_CRYPT_H
+#if defined(HAVE_CRYPT_R) && !defined(_GNU_SOURCE)
+/* Required for glibc to expose the crypt_r() function prototype. */
+#  define _GNU_SOURCE
+#  define _Py_GNU_SOURCE_FOR_CRYPT
+#endif
 #include <crypt.h>
+#ifdef _Py_GNU_SOURCE_FOR_CRYPT
+/* Don't leak the _GNU_SOURCE define to other headers. */
+#  undef _GNU_SOURCE
+#  undef _Py_GNU_SOURCE_FOR_CRYPT
+#endif
 #endif
 
 /* For size_t? */