diff --git a/sdk/compat/run-compat-tests.sh b/sdk/compat/run-compat-tests.sh
index 32ebc4f70..5b63d3b07 100755
--- a/sdk/compat/run-compat-tests.sh
+++ b/sdk/compat/run-compat-tests.sh
@@ -273,7 +273,7 @@ run_python_suite() {
         cd "$sdk_root/python"
         if ! command -v pdm >/dev/null 2>&1; then
             echo "Installing PDM..."
-            pip install pdm
+            pip install pdm 'unearth<0.19'
         fi
         pdm install --dev
         # `pdm run check` is deliberately not run: it lints the released SDK's
diff --git a/sdk/run-tests.sh b/sdk/run-tests.sh
index ff25c3755..2a86c45b5 100755
--- a/sdk/run-tests.sh
+++ b/sdk/run-tests.sh
@@ -35,7 +35,7 @@ pushd "$ROOT_DIR/python"
 # Ensure PDM is installed
 if ! command -v pdm &> /dev/null; then
     echo "Installing PDM..."
-    pip install pdm
+    pip install pdm 'unearth<0.19'
 fi
 # Install dependencies and setup environment using PDM
 pdm install --dev