diff --git a/tox.ini b/tox.ini
index 9025982..1a6a7b0 100644
--- a/tox.ini
+++ b/tox.ini
@@ -15,6 +15,11 @@ indexserver =
 # Suppress display of matplotlib plots generated during docs build
 setenv =
     clocale: LC_ALL = C
+    # Tests run in a temporary directory (see changedir below), so point the
+    # coverage data file back at the repo root. The OpenAstronomy tox workflow
+    # requires the .coverage file to be in the root to combine and upload it.
+    # https://github-actions-workflows.openastronomy.org/en/stable/tox.html#coverage
+    cov: COVERAGE_FILE = {toxinidir}/.coverage
 
 # Pass through the following environment variables which may be needed for the CI
 passenv = HOME, WINDIR, LC_ALL, LC_CTYPE, CC, CI, IS_CRON, ARCH_ON_CI