diff --git a/backend/jest.tsconfig.json b/backend/jest.tsconfig.json
new file mode 100644
index 000000000..19ff87bd2
--- /dev/null
+++ b/backend/jest.tsconfig.json
@@ -0,0 +1,8 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "rootDir": ".",
+    "isolatedModules": true
+  },
+  "include": ["src/**/*.ts", "test/**/*.ts"]
+}
\ No newline at end of file
diff --git a/backend/jest.tsconfig.json.license b/backend/jest.tsconfig.json.license
new file mode 100644
index 000000000..bbe7d178d
--- /dev/null
+++ b/backend/jest.tsconfig.json.license
@@ -0,0 +1,3 @@
+SPDX-FileCopyrightText: 2026 The HedgeDoc developers (see AUTHORS file)
+
+SPDX-License-Identifier: CC0-1.0
\ No newline at end of file
diff --git a/backend/package.json b/backend/package.json
index a815003a9..34ca100d5 100644
--- a/backend/package.json
+++ b/backend/package.json
@@ -116,7 +116,7 @@
       "^.+\\.(t|j)s$": [
         "ts-jest",
         {
-          "tsconfig": "test/tsconfig.json",
+          "tsconfig": "jest.tsconfig.json",
           "diagnostics": {
             "ignoreCodes": [
               151002
@@ -125,6 +125,10 @@
         }
       ]
     },
+    "transformIgnorePatterns": [
+      "/node_modules/",
+      "<rootDir>/../commons/dist/cjs/"
+    ],
     "coverageDirectory": "../coverage",
     "testEnvironment": "node",
     "reporters": [
diff --git a/backend/src/frontend-config/frontend-config.service.spec.ts b/backend/src/frontend-config/frontend-config.service.spec.ts
index 00557185c..de7d33489 100644
--- a/backend/src/frontend-config/frontend-config.service.spec.ts
+++ b/backend/src/frontend-config/frontend-config.service.spec.ts
@@ -153,6 +153,7 @@ describe('FrontendConfigService', () => {
             type: AuthProviderType.LDAP,
             providerName: authConfig.ldap[0].providerName,
             identifier: authConfig.ldap[0].identifier,
+            theme: null,
           });
         }
         if (authConfig.oidc.length > 0) {
@@ -162,6 +163,7 @@ describe('FrontendConfigService', () => {
             type: AuthProviderType.OIDC,
             providerName: authConfig.oidc[0].providerName,
             identifier: authConfig.oidc[0].identifier,
+            theme: null,
           });
         }
       });
diff --git a/backend/tsconfig.json b/backend/tsconfig.json
index 82609dcc2..ac28fe481 100644
--- a/backend/tsconfig.json
+++ b/backend/tsconfig.json
@@ -11,7 +11,6 @@
     "outDir": "./dist",
     "incremental": true,
     "strict": true,
-    "strictNullChecks": true,
     "strictPropertyInitialization": false,
     "resolveJsonModule": true,
     "useDefineForClassFields": false,