diff --git a/facetopology.c b/facetopology.c
index a63f4206..8617eb13 100644
--- a/facetopology.c
+++ b/facetopology.c
@@ -32,12 +32,12 @@
   along with OpenRS.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#include <stdlib.h>
-#include <math.h>
-#include <string.h>
 #include <assert.h>
-#include <stdio.h>
 #include <limits.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 
 #include "preprocess.h"
 #include "facetopology.h"