diff --git a/.github/workflows/python-tests.yml b/.github/workflows/python-tests.yml
index fa7844c..5cc48f2 100644
--- a/.github/workflows/python-tests.yml
+++ b/.github/workflows/python-tests.yml
@@ -68,20 +68,20 @@ jobs:
             python-version: '3.12'
             toxenv: py312-test-pytest82
           - os: macos-latest
-            python-version: '3.12'
-            toxenv: py312-test-pytest82
+            python-version: '3.13-dev'
+            toxenv: py312-test-pytest83
           - os: windows-latest
-            python-version: '3.12'
-            toxenv: py312-test-pytest82
+            python-version: '3.13-dev'
+            toxenv: py312-test-pytestdev
           - os: macos-latest
             python-version: '3.11'
             toxenv: py311-test-pytestdev
-          - os: windows-latest
-            python-version: '3.11'
-            toxenv: py311-test-pytestdev
           - os: ubuntu-latest
             python-version: '3.12'
             toxenv: py312-test-pytestdev-numpydev
+          - os: ubuntu-latest
+            python-version: '3.13-dev'
+            toxenv: py313-test-pytestdev
 
     steps:
     - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332  # v4.1.7
diff --git a/CHANGES.rst b/CHANGES.rst
index 5c64b01..30a03a6 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -2,6 +2,7 @@
 ==================
 
 - Fixing output update for multiline code. [#253]
+- Fixing Python 3.13 compatibility. [#260]
 - Dropped ``setuptools`` as a runtime dependency. [#258]
 
 1.2.1 (2024-03-09)
diff --git a/pytest_doctestplus/plugin.py b/pytest_doctestplus/plugin.py
index f9c3a0c..5538c53 100644
--- a/pytest_doctestplus/plugin.py
+++ b/pytest_doctestplus/plugin.py
@@ -900,7 +900,8 @@ def write_modified_file(fname, new_fname, changes):
         lineno = change["test_lineno"] + change["example_lineno"]
         lineno += change["source"].count("\n")
 
-        indentation = " " * change["nindent"]
+        indentation = len(text[lineno-1]) - len(text[lineno-1].lstrip())
+        indentation = text[lineno-1][:indentation]
         want = indent(change["want"], indentation, lambda x: True)
         # Replace fully blank lines with the required `<BLANKLINE>`
         # (May need to do this also if line contains only whitespace)
diff --git a/tox.ini b/tox.ini
index f632ccd..3661c92 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 envlist =
-    py{38,39,310,311,312}-test
+    py{38,39,310,311,312,313}-test
     codestyle
 requires =
     setuptools >= 30.3.0
@@ -29,6 +29,7 @@ deps =
     pytest80: pytest==8.0.*
     pytest81: pytest==8.1.*
     pytest82: pytest==8.2.*
+    pytest83: pytest==8.3.*
     pytestdev: git+https://github.com/pytest-dev/pytest#egg=pytest
     numpydev: numpy>=0.0.dev0