diff --git a/frontend/src/api/backend-url-cases.json b/frontend/src/api/backend-url-cases.json
index 5391a1ed..6648ede9 100644
--- a/frontend/src/api/backend-url-cases.json
+++ b/frontend/src/api/backend-url-cases.json
@@ -3,6 +3,8 @@
   { "value": "/", "valid": true },
   { "value": "/api", "valid": true },
   { "value": "/api/", "valid": true },
+  { "value": "/datamart-builder/api", "valid": true },
+  { "value": "/datamart-builder/api/", "valid": true },
   { "value": "http://localhost:8787", "valid": true },
   { "value": "https://api.example.test/v1", "valid": true },
   { "value": "https://api.example.test/base/path/", "valid": true },
diff --git a/frontend/src/api/backend-url-policy.json b/frontend/src/api/backend-url-policy.json
index b97c5da2..05087223 100644
--- a/frontend/src/api/backend-url-policy.json
+++ b/frontend/src/api/backend-url-policy.json
@@ -1,5 +1,5 @@
 {
-  "relativeBases": ["", "/", "/api", "/api/"],
+  "relativeBases": ["", "/", "/api", "/api/", "/datamart-builder/api", "/datamart-builder/api/"],
   "absolutePattern": "^https?://(?:\\[[0-9A-Fa-f:.]+\\]|[A-Za-z0-9](?:[A-Za-z0-9.-]*[A-Za-z0-9])?)(?::[0-9]+)?(?:/[^\\s?#]*)?/?$",
   "maxPort": 65535,
   "queryAllowed": false,