diff --git a/monai/transforms/utils.py b/monai/transforms/utils.py
index ea3577159d..111bfa1102 100644
--- a/monai/transforms/utils.py
+++ b/monai/transforms/utils.py
@@ -569,9 +569,10 @@ def generate_label_classes_crop_centers(
         raise ValueError(f"ratios should not contain negative number, got {ratios_}.")
 
     for i, array in enumerate(indices):
-        if len(array) == 0 and warn:
-            warnings.warn(f"no available indices of class {i} to crop, set the crop ratio of this class to zero.")
+        if len(array) == 0:
             ratios_[i] = 0
+            if warn:
+                warnings.warn(f"no available indices of class {i} to crop, set the crop ratio of this class to zero.")
 
     centers = []
     classes = rand_state.choice(len(ratios_), size=num_samples, p=np.asarray(ratios_) / np.sum(ratios_))