prevent prepocessor comparisons against empty tokens

1 files changed, 5 insertions, 0 deletions

diff --git a/math.h b/math.h
index 6ea714e..c8f04c5 100644
--- a/math.h
+++ b/math.h
@@ -27,6 +27,11 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */
 
+#if defined _XOPEN_SOURCE && _XOPEN_SOURCE - 1 < 0
+#undef _XOPEN_SOURCE
+#define _XOPEN_SOURCE 400
+#endif
+
 #if defined _XOPEN_SOURCE && !defined _POSIX_C_SOURCE
 #	if (_XOPEN_SOURCE >= 700)
 #		define _POSIX_C_SOURCE 200809L