diff --git a/CHANGELOG.md b/CHANGELOG.md
index 65abbd3d00..b897f4cb31 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
+### Fixed
+- Fix default `histfunc` value for `px.Histogram2dContour` when no arguments are provided; it now correctly defaults to `'sum'`, matching the behavior of `px.Histogram2d()` [[#5342](https://github.com/plotly/plotly.py/pull/5342)], with thanks to @gmjw for the contribution!
 
 ## [7.1.0] - 2026-09-15
 
diff --git a/plotly/express/_core.py b/plotly/express/_core.py
index 027df9e5aa..8b154672b7 100644
--- a/plotly/express/_core.py
+++ b/plotly/express/_core.py
@@ -2332,7 +2332,7 @@ def infer_config(args, constructor, trace_patch, layout_patch):
                 layout_patch[mode] = "group"
 
     if (
-        constructor == go.Histogram2d
+        constructor in [go.Histogram2d, go.Histogram2dContour]
         and args["z"] is not None
         and args["histfunc"] is None
     ):