diff --git a/enc/unicode.c b/enc/unicode.c
index beb5fa3..3b8fbc7 100644
--- a/enc/unicode.c
+++ b/enc/unicode.c
@@ -2080,7 +2080,7 @@ onigenc_utf16_32_get_ctype_code_range(OnigCtype ctype, OnigCodePoint* sb_out,
 
 #include "ruby/st.h"
 
-#define PROPERTY_NAME_MAX_SIZE    MAX_WORD_LENGTH
+#define PROPERTY_NAME_MAX_SIZE    (MAX_WORD_LENGTH + 1)
 
 extern int
 onigenc_unicode_property_name_to_ctype(OnigEncoding enc, UChar* name, UChar* end)