diff --git a/nilearn/plotting/js_plotting_utils.py b/nilearn/plotting/js_plotting_utils.py
index 5e41e2ae54..90e4efa222 100644
--- a/nilearn/plotting/js_plotting_utils.py
+++ b/nilearn/plotting/js_plotting_utils.py
@@ -87,6 +87,8 @@ def colorscale(cmap, values, threshold=None, symmetric_cmap=True,
         vmin = 0
     if vmax is None:
         vmax = abs_values.max()
+    # cast to float to avoid TypeError if vmax is a numpy boolean
+    vmax = float(vmax)
     if symmetric_cmap:
         vmin = - vmax
     if vmin is None:
diff --git a/nilearn/plotting/tests/test_js_plotting_utils.py b/nilearn/plotting/tests/test_js_plotting_utils.py
index 06bc608b54..ffd6555ee4 100644
--- a/nilearn/plotting/tests/test_js_plotting_utils.py
+++ b/nilearn/plotting/tests/test_js_plotting_utils.py
@@ -62,6 +62,7 @@ def test_colorscale_no_threshold():
     assert colors['cmap'].N == 256
     assert (colors['norm'].vmax, colors['norm'].vmin) == (13, -13)
     assert colors['abs_threshold'] is None
+    colors = js_plotting_utils.colorscale(cmap, values > 0, .5)
 
 
 def test_colorscale_threshold_0():