diff --git a/changelog.d/4326.bugfix b/changelog.d/4326.bugfix
new file mode 100644
index 0000000000..acce6266b8
--- /dev/null
+++ b/changelog.d/4326.bugfix
@@ -0,0 +1,2 @@
+Avoid packaging _trial_temp directory in -py3 debian packages
+
diff --git a/debian/build_virtualenv b/debian/build_virtualenv
index e9ef245476..83346c40f1 100755
--- a/debian/build_virtualenv
+++ b/debian/build_virtualenv
@@ -42,8 +42,7 @@ tmpdir=`mktemp -d`
 trap "rm -r $tmpdir" EXIT
 
 cp -r tests "$tmpdir"
-cd debian/matrix-synapse-py3
 
 PYTHONPATH="$tmpdir" \
-    ./opt/venvs/matrix-synapse/bin/python \
+    debian/matrix-synapse-py3/opt/venvs/matrix-synapse/bin/python \
         -B -m twisted.trial --reporter=text -j2 tests