diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index e871e265c..199ad7f82 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -43,10 +43,12 @@ jobs:
       matrix:
         include:
           - os: ubuntu-latest
-            py: "3.12"
+            py: "3.13-dev"
           - os: windows-latest
-            py: "3.12"
+            py: "3.13-dev"
           - os: macos-latest
+            py: "3.13-dev"
+          - os: ubuntu-latest
             py: "3.12"
           - os: ubuntu-latest
             py: "3.11"
diff --git a/CHANGELOG.md b/CHANGELOG.md
index c30cb988c..39d1eae6f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,8 @@
   ([#7073](https://github.com/mitmproxy/mitmproxy/pull/7073), @mhils)
 - Fix a bug where fragmented QUIC client hellos were not handled properly.
   ([#7067](https://github.com/mitmproxy/mitmproxy/pull/7067), @errorxyz)
+- mitmproxy now officially supports Python 3.13.
+  ([#6934](https://github.com/mitmproxy/mitmproxy/pull/6934), @mhils)
 
 ## 02 August 2024: mitmproxy 10.4.2
 
diff --git a/mitmproxy/net/encoding.py b/mitmproxy/net/encoding.py
index 95fd23bf4..ca4a71ace 100644
--- a/mitmproxy/net/encoding.py
+++ b/mitmproxy/net/encoding.py
@@ -147,16 +147,15 @@ def identity(content):
 def decode_gzip(content: bytes) -> bytes:
     if not content:
         return b""
-    gfile = gzip.GzipFile(fileobj=BytesIO(content))
-    return gfile.read()
+    with gzip.GzipFile(fileobj=BytesIO(content)) as f:
+        return f.read()
 
 
 def encode_gzip(content: bytes) -> bytes:
     s = BytesIO()
     # set mtime to 0 so that gzip encoding is deterministic.
-    gf = gzip.GzipFile(fileobj=s, mode="wb", mtime=0)
-    gf.write(content)
-    gf.close()
+    with gzip.GzipFile(fileobj=s, mode="wb", mtime=0) as f:
+        f.write(content)
     return s.getvalue()
 
 
diff --git a/pyproject.toml b/pyproject.toml
index c76b40873..dd4ecda51 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -19,6 +19,7 @@ classifiers = [
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
     "Programming Language :: Python :: Implementation :: CPython",
     "Topic :: Security",
     "Topic :: Internet :: WWW/HTTP",
@@ -65,8 +66,8 @@ dev = [
     "click>=7.0,<=8.1.7",
     "hypothesis>=6.104.2,<=6.108.5",
     "pdoc>=14.5.1,<=14.6.0",
-    "pyinstaller==6.9.0",
-    "pyinstaller-hooks-contrib==2024.7",
+    "pyinstaller==6.10.0",
+    "pyinstaller-hooks-contrib==2024.8",
     "pytest-asyncio>=0.23.6,<=0.23.8",
     "pytest-cov>=5.0.0,<=5.0.0",
     "pytest-timeout>=2.3.1,<=2.3.1",