diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index ac571724..e3f6ebda 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -6,6 +6,8 @@ v3.1.1
 
 *Release date: In development*
 
+- Upgrade Sphinx version from 4.* to 7.* to fix readthedocs theme format
+
 v3.1.0
 ------
 
diff --git a/docs/conf.py b/docs/conf.py
index 7777b10b..818c415d 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -55,6 +55,7 @@
     'sphinx.ext.todo',
     'sphinx.ext.ifconfig',
     'sphinx.ext.viewcode',
+    'sphinx_rtd_theme',
 ]
 
 # Add any paths that contain templates here, relative to this directory.
@@ -127,7 +128,9 @@
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
-html_theme = 'default'
+#html_theme = 'default'
+import sphinx_rtd_theme
+html_theme = "sphinx_rtd_theme"
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
diff --git a/docs/requirements.txt b/docs/requirements.txt
index f3415ccf..77b8ac80 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,3 +1,3 @@
-Sphinx==4.*
-sphinx_rtd_theme==1.*
-readthedocs-sphinx-search==0.1.*
+Sphinx~=7.2
+sphinx_rtd_theme~=1.3
+readthedocs-sphinx-search~=0.3