diff --git a/glue_plotly/common/image.py b/glue_plotly/common/image.py
index 385dae4..a3b47ac 100644
--- a/glue_plotly/common/image.py
+++ b/glue_plotly/common/image.py
@@ -181,7 +181,7 @@ def colorscale_info(layer_state, interval, contrast_bias):
     unmapped_space = np.linspace(0, 1, 60)
     mapped_space = np.linspace(mapped_bounds[0], mapped_bounds[1], 60)
     color_space = [cmap(b)[:3] for b in mapped_space]
-    color_values = [tuple(256 * v for v in p) for p in color_space]
+    color_values = [tuple(float(256 * v) for v in p) for p in color_space]
     colorscale = [[0, 'rgb{0}'.format(color_values[0])]] + \
                  [[u, 'rgb{0}'.format(c)] for u, c in zip(unmapped_space, color_values)] + \
                  [[1, 'rgb{0}'.format(color_values[-1])]]
diff --git a/glue_plotly/common/tests/test_dendrogram.py b/glue_plotly/common/tests/test_dendrogram.py
index 73c301b..f1dfcbd 100644
--- a/glue_plotly/common/tests/test_dendrogram.py
+++ b/glue_plotly/common/tests/test_dendrogram.py
@@ -4,6 +4,7 @@
 
 from glue.config import settings
 from glue.core import Data
+from glue.tests.helpers import make_skipper
 from glue_qt.app import GlueApplication
 from glue_qt.plugins.dendro_viewer import DendrogramViewer
 
@@ -12,6 +13,11 @@
 from glue_plotly.common.dendrogram import trace_for_layer, x_axis
 
 
+NUMPY_LT_2, requires_numpy_lt2 = make_skipper('numpy', version='2.0', skip_if='ge')
+
+
+# Workaround until for the issue solved in https://github.com/glue-viz/glue-qt/pull/19
+@requires_numpy_lt2
 class TestDendrogram:
 
     def setup_method(self, method):
diff --git a/glue_plotly/html_exporters/qt/tests/test_dendrogram.py b/glue_plotly/html_exporters/qt/tests/test_dendrogram.py
index 299dea9..9a86ac2 100644
--- a/glue_plotly/html_exporters/qt/tests/test_dendrogram.py
+++ b/glue_plotly/html_exporters/qt/tests/test_dendrogram.py
@@ -1,6 +1,7 @@
 import os
 
 from glue.core import Data
+from glue.tests.helpers import make_skipper
 
 from pytest import importorskip
 
@@ -11,6 +12,11 @@
 from .test_base import TestQtExporter  # noqa: E402
 
 
+NUMPY_LT_2, requires_numpy_lt2 = make_skipper('numpy', version='2.0', skip_if='ge')
+
+
+# Workaround until for the issue solved in https://github.com/glue-viz/glue-qt/pull/19
+@requires_numpy_lt2
 class TestDendrogram(TestQtExporter):
 
     viewer_type = DendrogramViewer