diff --git a/imperative/python/megengine/quantization/observer.py b/imperative/python/megengine/quantization/observer.py
index 26d5465d..b1c59905 100644
--- a/imperative/python/megengine/quantization/observer.py
+++ b/imperative/python/megengine/quantization/observer.py
@@ -171,7 +171,7 @@ class HistogramObserver(MinMaxObserver):
         self.bins = bins
         self.upsample_rate = upsample_rate
         self.dst_nbins = _metadata_dict[dtype].qmax - _metadata_dict[dtype].qmin + 1
-        self.histogram = Tensor([-1] + [0.0] * (bins - 1))
+        self.histogram = Tensor([-1] + [0.0] * (bins - 1), dtype="float32")
 
     def _non_linear_param_search(self):
         r"""Non-linear parameter search.
@@ -304,8 +304,8 @@ class HistogramObserver(MinMaxObserver):
             start_bin = next_start_bin
             end_bin = next_end_bin
 
-        new_min = self.min_val + bin_width * start_bin
-        new_max = self.min_val + bin_width * (end_bin + 1)
+        new_min = self.min_val + Tensor(bin_width * start_bin, dtype=np.float32)
+        new_max = self.min_val + Tensor(bin_width * (end_bin + 1), dtype=np.float32)
         return new_min, new_max
 
     def get_qparams(self):