diff --git a/respeaker_ros/scripts/respeaker_node.py b/respeaker_ros/scripts/respeaker_node.py
index 0fde85c40..261598444 100644
--- a/respeaker_ros/scripts/respeaker_node.py
+++ b/respeaker_ros/scripts/respeaker_node.py
@@ -410,7 +410,7 @@ def __init__(self):
             self.pub_speech_audio_raw = rospy.Publisher(
                 "speech_audio_raw", AudioData, queue_size=10)
             self.speech_raw_prefetch_bytes = int(
-                self.n_channel - 2
+                (self.n_channel - 2)
                 * self.speech_prefetch
                 * self.respeaker_audio.rate
                 * self.respeaker_audio.bitdepth / 8.0)