diff --git a/tools/shell/inc/shellTire.h b/tools/shell/inc/shellTire.h
index e87c3ee4f3..472f604a2c 100644
--- a/tools/shell/inc/shellTire.h
+++ b/tools/shell/inc/shellTire.h
@@ -19,8 +19,8 @@
 //
 // The prefix search tree is a efficient storage words and search words tree, it support 95 visible ascii code character
 //
-#define FIRST_ASCII 40   // first visible char is '0'
-#define LAST_ASCII  122  // last visilbe char is 'z'
+#define FIRST_ASCII 32   // first visible char is '0'
+#define LAST_ASCII  126  // last visilbe char is 'z'
 
 // capacity save char is 95
 #define CHAR_CNT     (LAST_ASCII - FIRST_ASCII + 1)
diff --git a/tools/shell/src/shellTire.c b/tools/shell/src/shellTire.c
index a8726f3126..8aa67457f2 100644
--- a/tools/shell/src/shellTire.c
+++ b/tools/shell/src/shellTire.c
@@ -95,7 +95,7 @@ bool insertToTree(STire* tire, char* word, int len) {
   STireNode** nodes = tire->root.d;
   for (int i = 0; i < len; i++) {
     m = word[i] - FIRST_ASCII;
-    if (m < 0 || m > CHAR_CNT) {
+    if (m < 0 || m >= CHAR_CNT) {
       return false;
     }