diff --git a/yolort/utils/visualizer.py b/yolort/utils/visualizer.py
index 8dea5182..93495479 100644
--- a/yolort/utils/visualizer.py
+++ b/yolort/utils/visualizer.py
@@ -64,7 +64,7 @@ def __init__(
         # Set dataset metadata (e.g. class names)
         self.metadata = None
         if metalabels is not None:
-            self.metadata = np.loadtxt(metalabels, dtype='str', delimiter='\n')
+            self.metadata = np.loadtxt(metalabels, dtype="str", delimiter="\n")
 
         self.scale = scale
         self.cpu_device = torch.device("cpu")