diff --git a/ext/mbstring/mbstring.c b/ext/mbstring/mbstring.c
index 30855b385a1..b22c494d634 100644
--- a/ext/mbstring/mbstring.c
+++ b/ext/mbstring/mbstring.c
@@ -2753,7 +2753,7 @@ PHP_FUNCTION(mb_convert_encoding)
 }
 /* }}} */
 
-static zend_string *mbstring_convert_case(int case_mode, const char *str, size_t str_len, const mbfl_encoding *enc)
+static zend_string *mbstring_convert_case(php_case_mode case_mode, const char *str, size_t str_len, const mbfl_encoding *enc)
 {
 	return php_unicode_convert_case(case_mode, str, str_len, enc, MBSTRG(current_filter_illegal_mode), MBSTRG(current_filter_illegal_substchar));
 }
@@ -2775,7 +2775,7 @@ PHP_FUNCTION(mb_convert_case)
 		RETURN_THROWS();
 	}
 
-	if (case_mode < 0 || case_mode > PHP_UNICODE_CASE_MODE_MAX) {
+	if (case_mode < 0 || case_mode >= PHP_UNICODE_CASE_MODE_MAX) {
 		zend_argument_value_error(2, "must be one of the MB_CASE_* constants");
 		RETURN_THROWS();
 	}
diff --git a/ext/mbstring/php_unicode.c b/ext/mbstring/php_unicode.c
index 23bf2f5399a..37552f66c11 100644
--- a/ext/mbstring/php_unicode.c
+++ b/ext/mbstring/php_unicode.c
@@ -238,7 +238,7 @@ static uint32_t *emit_special_casing_sequence(uint32_t w, uint32_t *out)
 	return out;
 }
 
-MBSTRING_API zend_string *php_unicode_convert_case(int case_mode, const char *srcstr, size_t in_len, const mbfl_encoding *src_encoding, int illegal_mode, int illegal_substchar)
+MBSTRING_API zend_string *php_unicode_convert_case(php_case_mode case_mode, const char *srcstr, size_t in_len, const mbfl_encoding *src_encoding, int illegal_mode, int illegal_substchar)
 {
 	/* A Unicode codepoint can expand out to up to 3 codepoints when uppercased, lowercased, or title cased
 	 * See http://www.unicode.org/Public/UNIDATA/SpecialCasing.txt */
diff --git a/ext/mbstring/php_unicode.h b/ext/mbstring/php_unicode.h
index 16496fbd125..be5dc110236 100644
--- a/ext/mbstring/php_unicode.h
+++ b/ext/mbstring/php_unicode.h
@@ -77,19 +77,21 @@
 MBSTRING_API bool php_unicode_is_prop(unsigned long code, ...);
 MBSTRING_API bool php_unicode_is_prop1(unsigned long code, int prop);
 
-MBSTRING_API zend_string *php_unicode_convert_case(
-		int case_mode, const char *srcstr, size_t srclen,
-		const mbfl_encoding *src_encoding, int illegal_mode, int illegal_substchar);
+typedef enum {
+	PHP_UNICODE_CASE_UPPER = 0,
+	PHP_UNICODE_CASE_LOWER,
+	PHP_UNICODE_CASE_TITLE,
+	PHP_UNICODE_CASE_FOLD,
+	PHP_UNICODE_CASE_UPPER_SIMPLE,
+	PHP_UNICODE_CASE_LOWER_SIMPLE,
+	PHP_UNICODE_CASE_TITLE_SIMPLE,
+	PHP_UNICODE_CASE_FOLD_SIMPLE,
+	PHP_UNICODE_CASE_MODE_MAX
+} php_case_mode;
 
-#define PHP_UNICODE_CASE_UPPER        0
-#define PHP_UNICODE_CASE_LOWER        1
-#define PHP_UNICODE_CASE_TITLE        2
-#define PHP_UNICODE_CASE_FOLD         3
-#define PHP_UNICODE_CASE_UPPER_SIMPLE 4
-#define PHP_UNICODE_CASE_LOWER_SIMPLE 5
-#define PHP_UNICODE_CASE_TITLE_SIMPLE 6
-#define PHP_UNICODE_CASE_FOLD_SIMPLE  7
-#define PHP_UNICODE_CASE_MODE_MAX     7
+MBSTRING_API zend_string *php_unicode_convert_case(
+		php_case_mode case_mode, const char *srcstr, size_t srclen,
+		const mbfl_encoding *src_encoding, int illegal_mode, int illegal_substchar);
 
 /* Optimize the common ASCII case for lower/upper */