diff --git a/runtime/core/frontend/fbank.h b/runtime/core/frontend/fbank.h
index f3e1d37211..133cbdb349 100644
--- a/runtime/core/frontend/fbank.h
+++ b/runtime/core/frontend/fbank.h
@@ -31,6 +31,8 @@ namespace wenet {
 // This code is based on kaldi Fbank implementation, please see
 // https://github.com/kaldi-asr/kaldi/blob/master/src/feat/feature-fbank.cc
 
+static const int kS16AbsMax = 1 << 15;
+
 enum class WindowType {
   kPovey = 0,
   kHanning,
@@ -265,7 +267,7 @@ class Fbank {
 
       if (scale_input_to_unit_) {
         for (int j = 0; j < frame_length_; ++j) {
-          data[j] = data[j] / S16_ABS_MAX;
+          data[j] = data[j] / kS16AbsMax;
         }
       }