diff --git a/plotly/express/_core.py b/plotly/express/_core.py
index ca3cf6dc5e..1b599cb43c 100644
--- a/plotly/express/_core.py
+++ b/plotly/express/_core.py
@@ -973,7 +973,7 @@ def make_trace_spec(args, constructor, attrs, trace_patch):
                 )
             else:
                 raise ValueError(
-                    f"Invalid value '{args['marginal_' + letter]}' for `marginal_{letter}`."
+                    f"Invalid value '{args['marginal_' + letter]}' for `marginal_{letter}`. "
                     "Supported marginal plot types are: 'rug', 'box', 'violin', 'histogram'."
                 )
             if "color" in attrs or "color" not in args: