diff --git a/py/lexer.c b/py/lexer.c
index af413021b1..8088697d54 100644
--- a/py/lexer.c
+++ b/py/lexer.c
@@ -471,7 +471,7 @@ static void mp_lexer_next_token_into(mp_lexer_t *lex, mp_token_t *tok, bool firs
                         case 'r': c = 0x0d; break;
                         case 'x':
                         {
-                            uint num;
+                            uint num = 0;
                             if (!get_hex(lex, 2, &num)) {
                                 // TODO error message
                                 assert(0);
diff --git a/py/vstr.c b/py/vstr.c
index 18e6d2d0a8..b2e46c89f9 100644
--- a/py/vstr.c
+++ b/py/vstr.c
@@ -190,6 +190,7 @@ void vstr_cut_tail(vstr_t *vstr, int len) {
     } else {
         vstr->len -= len;
     }
+    vstr->buf[vstr->len] = 0;
 }
 
 void vstr_printf(vstr_t *vstr, const char *fmt, ...) {