@@ -187,10 +187,12 @@
 	[OBJCFLAGS="$OBJCFLAGS -Wobjc-missing-property-synthesis"])
 AX_CHECK_COMPILER_FLAGS([-Watomic-properties -Werror], [
 	OBJCFLAGS="$OBJCFLAGS -Watomic-properties"
 	TESTS_OBJCFLAGS="$TESTS_OBJCFLAGS -Wno-atomic-properties"
 ])
+AX_CHECK_COMPILER_FLAGS([-Wnullable-to-nonnull-conversion -Werror],
+	[OBJCFLAGS="$OBJCFLAGS -Wnullable-to-nonnull-conversion"])
 
 AC_MSG_CHECKING(whether Objective C compiler supports properties)
 AC_TRY_COMPILE([
 	#ifdef __has_attribute
 	# if __has_attribute(objc_root_class)