diff --git a/Makefile.inc b/Makefile.inc
index ef565c2..3eaabaf 100644
--- a/Makefile.inc
+++ b/Makefile.inc
@@ -414,7 +414,7 @@
 CFLAGS_common += -pipe -g -nostdinc -std=gnu11
 CFLAGS_common += -nostdlib -Wall -Wundef -Wstrict-prototypes -Wmissing-prototypes
 CFLAGS_common += -Wwrite-strings -Wredundant-decls -Wno-trigraphs -Wimplicit-fallthrough
-CFLAGS_common += -Wshadow -Wdate-time -Wtype-limits -Wvla
+CFLAGS_common += -Wshadow -Wdate-time -Wtype-limits -Wvla -Wold-style-definition
 CFLAGS_common += -Wdangling-else
 CFLAGS_common += -fno-common -ffreestanding -fno-builtin -fomit-frame-pointer
 CFLAGS_common += -fstrict-aliasing -ffunction-sections -fdata-sections -fno-pie