diff --git a/py/emitinlinethumb.c b/py/emitinlinethumb.c
index 59cdc3aca6..bc120e8bed 100644
--- a/py/emitinlinethumb.c
+++ b/py/emitinlinethumb.c
@@ -363,8 +363,8 @@ STATIC void emit_inline_thumb_op(emit_inline_asm_t *emit, qstr op, mp_uint_t n_a
     // three_args =
     // "subs", RLO, RLO, I3, asm_thumb_subs_reg_reg_i3
 
-    const char *op_str = qstr_str(op);
-    mp_uint_t op_len = strlen(op_str);
+    mp_uint_t op_len;
+    const char *op_str = (const char*)qstr_data(op, &op_len);
 
     if (n_args == 0) {
         if (strcmp(op_str, "nop") == 0) {