diff --git a/Makefile b/Makefile
index 656f9df..b233f1c 100644
--- a/Makefile
+++ b/Makefile
@@ -9,7 +9,7 @@ LIBAS6502=   $(LIBAS6502_DIR)/libas6502.a
 LIBDIS6502_DIR= $(V6502_PREFIX)/dis6502
 LIBDIS6502=   $(LIBDIS6502_DIR)/libdis6502.a
 
-CFLAGS+=	-I$(V6502_PREFIX)
+CFLAGS+=	-I$(V6502_PREFIX) -std=c99
 LDFLAGS+=	-lcurses -ldis6502 -las6502 -lv6502 -L$(LIBV6502_DIR) -L$(LIBAS6502_DIR) -L $(LIBDIS6502_DIR)
 OBJS=		$(SRCS:.c=.o)