diff --git a/src/scanner.c b/src/scanner.c
index d5835856..47f231e2 100644
--- a/src/scanner.c
+++ b/src/scanner.c
@@ -67,6 +67,9 @@ typedef struct {
     Array(Heredoc) open_heredocs;
 } Scanner;
 
+static const int32_t ASCII_C0_CONTROL_MAX = 0x1f;
+static const int32_t ASCII_MAX = 0x7f;
+
 const char NON_IDENTIFIER_CHARS[] = {
     '\0', '\n', '\r', '\t', ' ', ':', ';', '`',  '"', '\'', '@', '$', '#', '.', ',', '|', '^', '&',
     '<',  '=',  '>',  '+',  '-', '*', '/', '\\', '%', '?',  '!', '~', '(', ')', '[', ']', '{', '}',
@@ -336,8 +339,14 @@ static inline bool scan_operator(TSLexer *lexer) {
     }
 }
 
-static inline bool is_iden_char(char c) {
-    return memchr(&NON_IDENTIFIER_CHARS, c, sizeof(NON_IDENTIFIER_CHARS)) == NULL;
+static inline bool is_iden_char(int32_t c) {
+    if (c <= ASCII_C0_CONTROL_MAX || iswspace(c)) {
+        return false;
+    }
+    if (c > ASCII_MAX) {
+        return true;
+    }
+    return memchr(&NON_IDENTIFIER_CHARS, (char)c, sizeof(NON_IDENTIFIER_CHARS)) == NULL;
 }
 
 static inline bool scan_symbol_identifier(TSLexer *lexer) {
@@ -350,13 +359,13 @@ static inline bool scan_symbol_identifier(TSLexer *lexer) {
         advance(lexer);
     }
 
-    if (is_iden_char((char)lexer->lookahead)) {
+    if (is_iden_char(lexer->lookahead)) {
         advance(lexer);
     } else if (!scan_operator(lexer)) {
         return false;
     }
 
-    while (is_iden_char((char)lexer->lookahead)) {
+    while (is_iden_char(lexer->lookahead)) {
         advance(lexer);
     }
 
@@ -656,7 +665,7 @@ static inline bool scan_short_interpolation(TSLexer *lexer, const bool has_conte
             if (lexer->lookahead == '@') {
                 advance(lexer);
             }
-            is_short_interpolation = is_iden_char((char)lexer->lookahead) && !iswdigit(lexer->lookahead);
+            is_short_interpolation = is_iden_char(lexer->lookahead) && !iswdigit(lexer->lookahead);
         }
 
         if (is_short_interpolation) {
diff --git a/test/corpus/literals.txt b/test/corpus/literals.txt
index b4f59a34..a469c809 100644
--- a/test/corpus/literals.txt
+++ b/test/corpus/literals.txt
@@ -673,7 +673,9 @@ interpolation
 
 "#{foo}"
 "foo#@foo"
+"foo#@言"
 "#@@foo"
+"#@@言"
 "#$foo"
 "#$%"
 "#$1"
@@ -694,6 +696,13 @@ interpolation
     (string_content)
     (interpolation
       (instance_variable)))
+  (string
+    (string_content)
+    (interpolation
+      (instance_variable)))
+  (string
+    (interpolation
+      (class_variable)))
   (string
     (interpolation
       (class_variable)))
@@ -2290,6 +2299,9 @@ Cß
 @äö
 @@äö
 :äö
+:言
+:你
+:일
 äö
 
 ---
@@ -2299,4 +2311,7 @@ Cß
   (instance_variable)
   (class_variable)
   (simple_symbol)
+  (simple_symbol)
+  (simple_symbol)
+  (simple_symbol)
   (identifier))