diff --git a/configure.ac b/configure.ac
index da6a261c..19e98cf9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -290,6 +290,7 @@ AX_CHECK_COMPILE_FLAG([$CWFLAGS -Wstrict-prototypes], [CWFLAGS="$CWFLAGS -Wstric
 AX_CHECK_COMPILE_FLAG([$CWFLAGS -Wswitch-enum], [CWFLAGS="$CWFLAGS -Wswitch-enum"])
 AX_CHECK_COMPILE_FLAG([$CWFLAGS -Wvariable-decl], [CWFLAGS="$CWFLAGS -Wvariable-decl"])
 AX_CHECK_COMPILE_FLAG([$CWFLAGS -Wno-type-limits], [CWFLAGS="$CWFLAGS -Wno-type-limits"])
+AX_CHECK_COMPILE_FLAG([$CWFLAGS -Wold-style-declaration], [CWFLAGS="$CWFLAGS -Wold-style-declaration"])
 
 AX_CHECK_LINK_FLAG([-Wl,-z,relro], [LDFLAGS="$LDFLAGS -Wl,-z,relro"])
 AX_CHECK_LINK_FLAG([-Wl,-z,now], [LDFLAGS="$LDFLAGS -Wl,-z,now"])