diff --git a/newsfragments/3966.bugfix b/newsfragments/3966.bugfix
new file mode 100644
index 000000000..ead94c47c
--- /dev/null
+++ b/newsfragments/3966.bugfix
@@ -0,0 +1 @@
+Fix incompatibility with newer versions of the transitive charset_normalizer dependency when using PyInstaller.
\ No newline at end of file
diff --git a/setup.py b/setup.py
index 3681dc441..a9b42d522 100644
--- a/setup.py
+++ b/setup.py
@@ -148,6 +148,13 @@ install_requires = [
     # for pid-file support
     "psutil",
     "filelock",
+
+    # treq needs requests, requests needs charset_normalizer,
+    # charset_normalizer breaks PyInstaller
+    # (https://github.com/Ousret/charset_normalizer/issues/253). So work around
+    # this by using a lower version number. Once upstream issue is fixed, or
+    # requests drops charset_normalizer, this can go away.
+    "charset_normalizer < 3",
 ]
 
 setup_requires = [