diff --git a/Makefile b/Makefile
index b2ba8126..192ab2db 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,8 @@
 .POSIX:
 
-REALCFLAGS =	${CFLAGS} -Wall -Iinclude -Iinclude/asm/gameboy -g -std=c99 \
-		-D_POSIX_C_SOURCE=200112L
+WARNFLAGS =	-Wall -Werror=implicit-int
+REALCFLAGS =	${CFLAGS} ${WARNFLAGS} -Iinclude -Iinclude/asm/gameboy -g \
+		-std=c99 -D_POSIX_C_SOURCE=200112L
 
 # User-defined variables
 PREFIX =	/usr/local