diff --git a/pkgs/development/python-modules/cairocffi/default.nix b/pkgs/development/python-modules/cairocffi/default.nix
index 0779eae1c92d..bbcdbfb5fff8 100644
--- a/pkgs/development/python-modules/cairocffi/default.nix
+++ b/pkgs/development/python-modules/cairocffi/default.nix
@@ -56,6 +56,10 @@ buildPythonPackage rec {
 
   pythonImportsCheck = [ "cairocffi" ];
 
+  # Cairo tries to load system fonts by default.
+  # It's surfaced as a Cairo "out of memory" error in tests.
+  __impureHostDeps = [ "/System/Library/Fonts" ];
+
   meta = with lib; {
     changelog = "https://github.com/Kozea/cairocffi/blob/v${version}/NEWS.rst";
     homepage = "https://github.com/SimonSapin/cairocffi";
diff --git a/pkgs/development/python-modules/pycairo/default.nix b/pkgs/development/python-modules/pycairo/default.nix
index b1f0e5eba83e..883a879d3b1f 100644
--- a/pkgs/development/python-modules/pycairo/default.nix
+++ b/pkgs/development/python-modules/pycairo/default.nix
@@ -37,6 +37,10 @@ buildPythonPackage rec {
 
   nativeCheckInputs = [ pytestCheckHook ];
 
+  # Cairo tries to load system fonts by default.
+  # It's surfaced as a Cairo "out of memory" error in tests.
+  __impureHostDeps = [ "/System/Library/Fonts" ];
+
   mesonFlags = [
     # This is only used for figuring out what version of Python is in
     # use, and related stuff like figuring out what the install prefix
diff --git a/pkgs/development/python-modules/pygal/default.nix b/pkgs/development/python-modules/pygal/default.nix
index 52265c6ae970..2585c7dda9f5 100644
--- a/pkgs/development/python-modules/pygal/default.nix
+++ b/pkgs/development/python-modules/pygal/default.nix
@@ -56,6 +56,10 @@ buildPythonPackage rec {
     export LANG=en_US.UTF-8
   '';
 
+  # Cairo tries to load system fonts by default.
+  # It's surfaced as a Cairo "out of memory" error in tests.
+  __impureHostDeps = [ "/System/Library/Fonts" ];
+
   postCheck = ''
     export LANG=${if stdenv.isDarwin then "en_US.UTF-8" else "C.UTF-8"}
   '';