diff --git a/src/kit/shell/inc/shellCommand.h b/src/kit/shell/inc/shellCommand.h
index 3094bdb9ddb1ccd9debdbca88a34197385deb367..a08c1f48d11a8cd0e51fa5fb2d05a16da96d38c9 100644
--- a/src/kit/shell/inc/shellCommand.h
+++ b/src/kit/shell/inc/shellCommand.h
@@ -45,7 +45,7 @@ extern void updateBuffer(Command *cmd);
 extern int isReadyGo(Command *cmd);
 extern void resetCommand(Command *cmd, const char s[]);
 
-int countPrefixOnes(char c);
+int countPrefixOnes(unsigned char c);
 void clearScreen(int ecmd_pos, int cursor_pos);
 void printChar(char c, int times);
 void positionCursor(int step, int direction);
diff --git a/src/kit/shell/src/shellCommand.c b/src/kit/shell/src/shellCommand.c
index 9173ab0efdae7e5900218b2ab256993df71b21dd..e1a3dfe10205715d8c5cf8677a5be60c1a478b05 100644
--- a/src/kit/shell/src/shellCommand.c
+++ b/src/kit/shell/src/shellCommand.c
@@ -26,7 +26,7 @@ typedef struct {
   char widthOnScreen;
 } UTFCodeInfo;
 
-int countPrefixOnes(char c) {
+int countPrefixOnes(unsigned char c) {
   unsigned char mask = 127;
   mask = ~mask;
   int ret = 0;
@@ -48,7 +48,7 @@ void getPrevCharSize(const char *str, int pos, int *size, int *width) {
   while (--pos >= 0) {
     *size += 1;
 
-    if (str[pos] > 0 || countPrefixOnes(str[pos]) > 1) break;
+    if (str[pos] > 0 || countPrefixOnes((unsigned char )str[pos]) > 1) break;
   }
 
   int rc = mbtowc(&wc, str + pos, MB_CUR_MAX);