diff --git a/Makefile b/Makefile
index 9d07bd6..e68eb27 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 CC = x86_64-w64-mingw32-gcc
-CFLAGS = -W -Wall -pedantic
+CFLAGS = -std=c99 -W -Wall -pedantic
 LIBS = -lole32 -lavrt