diff --git a/Makefile b/Makefile
index 784ebc9..e22e48b 100644
--- a/Makefile
+++ b/Makefile
@@ -14,6 +14,8 @@
 # License along with this program.  If not, see
 # <https://www.gnu.org/licenses/>.
 
+.POSIX:
+
 CFLAGS += -std=c11 -pedantic -Wall -Wextra
 CFLAGS += -O3 -flto
 CFLAGS += -D_XOPEN_SOURCE=700