diff --git a/.github/workflows/test-postgis.yml b/.github/workflows/test-postgis.yml
index d4a42d1..f3c2125 100644
--- a/.github/workflows/test-postgis.yml
+++ b/.github/workflows/test-postgis.yml
@@ -17,7 +17,11 @@ jobs:
     needs: lint
     strategy:
       matrix:
-        ckan-version: [2.9, 2.9-py2]
+        include:
+          - ckan-version: 2.9
+            harvester-version: 'master'
+          - ckan-version: 2.9-py2
+            harvester-version: '1.4.2'
       fail-fast: false
     
     name: CKAN ${{ matrix.ckan-version }}
@@ -56,7 +60,7 @@ jobs:
 
     - name: Install harvester
       run: |
-        git clone https://github.com/ckan/ckanext-harvest
+        git clone --branch ${{ matrix.harvester-version }} https://github.com/ckan/ckanext-harvest
         cd ckanext-harvest
         pip install -r pip-requirements.txt
         pip install -r dev-requirements.txt