diff --git a/mmseg/datasets/custom.py b/mmseg/datasets/custom.py
index 3eeb0dda80..fe29dcf9c0 100644
--- a/mmseg/datasets/custom.py
+++ b/mmseg/datasets/custom.py
@@ -349,7 +349,16 @@ def get_palette_for_custom_classes(self, class_names, palette=None):
 
         elif palette is None:
             if self.PALETTE is None:
+                # Get random state before set seed, and restore
+                # random state later.
+                # It will prevent loss of randomness, as the palette
+                # may be different in each iteration if not specified.
+                # See: https://github.com/open-mmlab/mmdetection/issues/5844
+                state = np.random.get_state()
+                np.random.seed(42)
+                # random palette
                 palette = np.random.randint(0, 255, size=(len(class_names), 3))
+                np.random.set_state(state)
             else:
                 palette = self.PALETTE
 
diff --git a/mmseg/models/segmentors/base.py b/mmseg/models/segmentors/base.py
index f0f320ffbf..9b22a7ca9b 100644
--- a/mmseg/models/segmentors/base.py
+++ b/mmseg/models/segmentors/base.py
@@ -245,8 +245,17 @@ def show_result(self,
         seg = result[0]
         if palette is None:
             if self.PALETTE is None:
+                # Get random state before set seed,
+                # and restore random state later.
+                # It will prevent loss of randomness, as the palette
+                # may be different in each iteration if not specified.
+                # See: https://github.com/open-mmlab/mmdetection/issues/5844
+                state = np.random.get_state()
+                np.random.seed(42)
+                # random palette
                 palette = np.random.randint(
                     0, 255, size=(len(self.CLASSES), 3))
+                np.random.set_state(state)
             else:
                 palette = self.PALETTE
         palette = np.array(palette)