diff --git a/mrbgems/mruby-bin-mirb/tools/mirb/mirb_buffer.c b/mrbgems/mruby-bin-mirb/tools/mirb/mirb_buffer.c
index 92d3e5df4..411f6fee2 100644
--- a/mrbgems/mruby-bin-mirb/tools/mirb/mirb_buffer.c
+++ b/mrbgems/mruby-bin-mirb/tools/mirb/mirb_buffer.c
@@ -8,7 +8,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <ctype.h>
 
 #ifdef MRB_UTF8_STRING
 /*
@@ -782,15 +781,6 @@ mirb_buffer_cursor_finish(mirb_buffer *buf)
   buf->cursor_col = buf->lines[buf->cursor_line].len;
 }
 
-/*
- * Helper: Check if character is word character
- */
-static mrb_bool
-is_word_char(char c)
-{
-  return isalnum((unsigned char)c) || c == '_';
-}
-
 /*
  * Move cursor back one word
  */
@@ -810,7 +800,7 @@ mirb_buffer_cursor_word_back(mirb_buffer *buf)
     }
 
     char c = buf->lines[buf->cursor_line].data[buf->cursor_col - 1];
-    if (is_word_char(c)) break;
+    if (mirb_is_word_char(c)) break;
     buf->cursor_col--;
     moved = TRUE;
   }
@@ -818,7 +808,7 @@ mirb_buffer_cursor_word_back(mirb_buffer *buf)
   /* Move through word chars */
   while (buf->cursor_col > 0) {
     char c = buf->lines[buf->cursor_line].data[buf->cursor_col - 1];
-    if (!is_word_char(c)) break;
+    if (!mirb_is_word_char(c)) break;
     buf->cursor_col--;
     moved = TRUE;
   }
@@ -837,7 +827,7 @@ mirb_buffer_cursor_word_forward(mirb_buffer *buf)
 
   /* Move through current word chars */
   while (buf->cursor_col < line->len) {
-    if (!is_word_char(line->data[buf->cursor_col])) break;
+    if (!mirb_is_word_char(line->data[buf->cursor_col])) break;
     buf->cursor_col++;
     moved = TRUE;
   }
@@ -853,7 +843,7 @@ mirb_buffer_cursor_word_forward(mirb_buffer *buf)
       continue;
     }
 
-    if (is_word_char(line->data[buf->cursor_col])) break;
+    if (mirb_is_word_char(line->data[buf->cursor_col])) break;
     buf->cursor_col++;
     moved = TRUE;
   }
@@ -960,12 +950,12 @@ mirb_buffer_kill_word_forward(mirb_buffer *buf)
   size_t end_col = start_col;
 
   /* Skip word chars */
-  while (end_col < line->len && is_word_char(line->data[end_col])) {
+  while (end_col < line->len && mirb_is_word_char(line->data[end_col])) {
     end_col++;
   }
 
   /* Skip non-word chars */
-  while (end_col < line->len && !is_word_char(line->data[end_col])) {
+  while (end_col < line->len && !mirb_is_word_char(line->data[end_col])) {
     end_col++;
   }
 
diff --git a/mrbgems/mruby-bin-mirb/tools/mirb/mirb_buffer.h b/mrbgems/mruby-bin-mirb/tools/mirb/mirb_buffer.h
index 5c1164e89..dd6d0b122 100644
--- a/mrbgems/mruby-bin-mirb/tools/mirb/mirb_buffer.h
+++ b/mrbgems/mruby-bin-mirb/tools/mirb/mirb_buffer.h
@@ -182,4 +182,14 @@ size_t mirb_buffer_line_len(mirb_buffer *buf, size_t index);
  */
 size_t mirb_buffer_cursor_display_col(mirb_buffer *buf);
 
+/*
+ * Check if character is a word character (alphanumeric or underscore)
+ */
+static inline mrb_bool
+mirb_is_word_char(char c)
+{
+  return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') ||
+         (c >= '0' && c <= '9') || c == '_';
+}
+
 #endif /* MIRB_BUFFER_H */
diff --git a/mrbgems/mruby-bin-mirb/tools/mirb/mirb_editor.c b/mrbgems/mruby-bin-mirb/tools/mirb/mirb_editor.c
index a350a56cb..b397baa7d 100644
--- a/mrbgems/mruby-bin-mirb/tools/mirb/mirb_editor.c
+++ b/mrbgems/mruby-bin-mirb/tools/mirb/mirb_editor.c
@@ -11,7 +11,6 @@
 
 /* ANSI color codes */
 #define COLOR_GREEN   "\033[32m"
-#define COLOR_RESET   "\033[0m"
 
 /*
  * Check if line contains only whitespace before given column
diff --git a/mrbgems/mruby-bin-mirb/tools/mirb/mirb_highlight.c b/mrbgems/mruby-bin-mirb/tools/mirb/mirb_highlight.c
index 132a8f35e..44b4bb8d2 100644
--- a/mrbgems/mruby-bin-mirb/tools/mirb/mirb_highlight.c
+++ b/mrbgems/mruby-bin-mirb/tools/mirb/mirb_highlight.c
@@ -5,11 +5,11 @@
 */
 
 #include "mirb_highlight.h"
+#include "mirb_buffer.h"
 #include "mirb_term.h"
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
-#include <ctype.h>
 
 /* ANSI color codes - using standard 16-color palette for compatibility */
 
@@ -41,8 +41,6 @@
 #define LIGHT_ERROR    "\033[31m"    /* red */
 #define LIGHT_ARROW    "\033[90m"    /* gray */
 
-#define COLOR_RESET    "\033[0m"
-
 /* Keyword list - sorted alphabetically for bsearch, NULL-terminated */
 const char *mirb_keywords[] = {
   "BEGIN", "END", "__ENCODING__", "__FILE__", "__LINE__",
@@ -72,13 +70,6 @@ is_keyword(const char *word, size_t len)
   return bsearch(buf, mirb_keywords, mirb_num_keywords, sizeof(mirb_keywords[0]), keyword_cmp) != NULL;
 }
 
-static mrb_bool
-is_word_char(char c)
-{
-  return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') ||
-         (c >= '0' && c <= '9') || c == '_';
-}
-
 static mrb_bool
 is_word_start(char c)
 {
@@ -365,7 +356,7 @@ mirb_highlight_print_line(mirb_highlighter *hl, const char *line)
       }
       else {
         /* Regular symbol */
-        while (*p && (is_word_char(*p) || *p == '?' || *p == '!')) p++;
+        while (*p && (mirb_is_word_char(*p) || *p == '?' || *p == '!')) p++;
       }
       print_colored(hl, token_start, (size_t)(p - token_start), MIRB_TOK_SYMBOL);
       continue;
@@ -375,7 +366,7 @@ mirb_highlight_print_line(mirb_highlighter *hl, const char *line)
     if (*p == '@') {
       token_start = p++;
       if (*p == '@') p++;  /* @@class_var */
-      while (*p && is_word_char(*p)) p++;
+      while (*p && mirb_is_word_char(*p)) p++;
       print_colored(hl, token_start, (size_t)(p - token_start), MIRB_TOK_IVAR);
       continue;
     }
@@ -384,11 +375,11 @@ mirb_highlight_print_line(mirb_highlighter *hl, const char *line)
     if (*p == '$') {
       token_start = p++;
       /* Special globals like $!, $?, $1, etc. */
-      if (*p && !is_word_char(*p) && *p != ' ') {
+      if (*p && !mirb_is_word_char(*p) && *p != ' ') {
         p++;
       }
       else {
-        while (*p && is_word_char(*p)) p++;
+        while (*p && mirb_is_word_char(*p)) p++;
       }
       print_colored(hl, token_start, (size_t)(p - token_start), MIRB_TOK_GVAR);
       continue;
@@ -396,7 +387,7 @@ mirb_highlight_print_line(mirb_highlighter *hl, const char *line)
 
     /* Numbers */
     if ((*p >= '0' && *p <= '9') ||
-        (*p == '-' && p[1] >= '0' && p[1] <= '9' && (p == line || !is_word_char(p[-1])))) {
+        (*p == '-' && p[1] >= '0' && p[1] <= '9' && (p == line || !mirb_is_word_char(p[-1])))) {
       token_start = p;
       if (*p == '-') p++;
       if (*p == '0' && (p[1] == 'x' || p[1] == 'X')) {
@@ -440,7 +431,7 @@ mirb_highlight_print_line(mirb_highlighter *hl, const char *line)
       mrb_bool is_const = is_upper(*p);
       /* Check if preceded by dot (method call like obj.class) */
       mrb_bool after_dot = (token_start > line && token_start[-1] == '.');
-      while (*p && (is_word_char(*p) || *p == '?' || *p == '!')) p++;
+      while (*p && (mirb_is_word_char(*p) || *p == '?' || *p == '!')) p++;
 
       size_t len = (size_t)(p - token_start);
 
diff --git a/mrbgems/mruby-bin-mirb/tools/mirb/mirb_highlight.h b/mrbgems/mruby-bin-mirb/tools/mirb/mirb_highlight.h
index 3fab33a94..06d9e9a11 100644
--- a/mrbgems/mruby-bin-mirb/tools/mirb/mirb_highlight.h
+++ b/mrbgems/mruby-bin-mirb/tools/mirb/mirb_highlight.h
@@ -98,4 +98,7 @@ void mirb_highlight_print_result(mirb_highlighter *hl, const char *result);
  */
 void mirb_highlight_print_error(mirb_highlighter *hl, const char *error);
 
+/* Common ANSI reset code shared across modules */
+#define COLOR_RESET "\033[0m"
+
 #endif /* MIRB_HIGHLIGHT_H */