diff --git a/modoboa/pdfcredentials/api/v2/serializers.py b/modoboa/pdfcredentials/api/v2/serializers.py
index 0a0bab668..ffb8dcf4b 100644
--- a/modoboa/pdfcredentials/api/v2/serializers.py
+++ b/modoboa/pdfcredentials/api/v2/serializers.py
@@ -44,10 +44,12 @@ class PDFCredentialsSettingsSerializer(serializers.Serializer):
 
     def validate(self, data):
         """Check that directory exists."""
-        enabled_pdfcredentials = data.get("enabled_pdfcredentials", False)
+        enabled_pdfcredentials = data.get("enabled_pdfcredentials", None)
         condition = (enabled_pdfcredentials or
-                     param_tools.get_global_parameter("enabled_pdfcredentials")
+                     (enabled_pdfcredentials is None and
+                      param_tools.get_global_parameter("enabled_pdfcredentials")
                      )
+                    )
         if condition:
             storage_dir = data.get("storage_dir", None)
             if storage_dir is not None:
diff --git a/modoboa/pdfcredentials/api/v2/tests.py b/modoboa/pdfcredentials/api/v2/tests.py
index 2c3d79817..88cb981c3 100644
--- a/modoboa/pdfcredentials/api/v2/tests.py
+++ b/modoboa/pdfcredentials/api/v2/tests.py
@@ -170,12 +170,19 @@ class PDFCredentialViewTestCase(ModoAPITestCase):
         self.set_global_parameter("storage_dir", "/nonexistentdir")
         self.set_global_parameter("enabled_pdfcredentials", False)
         url = reverse("v2:parameter-detail", args=["pdfcredentials"])
+        data = {
+                "webpanel_url": "http://localhost",
+                "smtp_server_address": "mail.localhost",
+                "imap_server_address": "mail.localhost",
+               }
+
         # Test that we can't activate it without providing a valid storage dir.
-        data = {"enabled_pdfcredentials": True}
+        data["enabled_pdfcredentials"] = True
         resp = self.client.put(url, data, format="json")
         self.assertEqual(resp.status_code, 400)
+        self.assertIn(b"Directory not found", resp.content)
         # Test that we can disable it even if the directory is not right.
-        self.set_global_parameter("enabled_pdfcredentials", False)
-        data = {"enabled_pdfcredentials": True}
+        self.set_global_parameter("enabled_pdfcredentials", True)
+        data["enabled_pdfcredentials"] = False
         resp = self.client.put(url, data, format="json")
         self.assertEqual(resp.status_code, 200)