diff --git a/ext/mbstring/php_unicode.c b/ext/mbstring/php_unicode.c
index b53339a2b02..a84a5b724d8 100644
--- a/ext/mbstring/php_unicode.c
+++ b/ext/mbstring/php_unicode.c
@@ -304,7 +304,7 @@ MBSTRING_API char *php_unicode_convert_case(int case_mode, const char *srcstr, s
 			for (i = 0; i < unicode_len; i+=4) {
 				int res = php_unicode_is_prop(
 					BE_ARY_TO_UINT32(&unicode_ptr[i]),
-					UC_MN|UC_ME|UC_CF|UC_LM|UC_SK|UC_LU|UC_LL|UC_LT, 0);
+					UC_MN|UC_ME|UC_CF|UC_LM|UC_SK|UC_LU|UC_LL|UC_LT|UC_PO|UC_OS, 0);
 				if (mode) {
 					if (res) {
 						UINT32_TO_BE_ARY(&unicode_ptr[i],