diff --git a/src/main/library-path-config.ts b/src/main/library-path-config.ts
index 3dbf49f..422d1e5 100644
--- a/src/main/library-path-config.ts
+++ b/src/main/library-path-config.ts
@@ -18,6 +18,21 @@ function isPlainObject(value: unknown): value is Record<string, unknown> {
     return typeof value === 'object' && value !== null && !Array.isArray(value);
 }
 
+/**
+ * Normalize an administrator-supplied DLC_DIR and accept it only when it
+ * already names a directory. Invalid overrides must not shadow config.json.
+ */
+export function normalizeExplicitLibraryPath(rawPath?: string): string | undefined {
+    const candidate = (rawPath || '').trim();
+    if (!candidate) return undefined;
+
+    try {
+        return fs.statSync(candidate).isDirectory() ? candidate : undefined;
+    } catch {
+        return undefined;
+    }
+}
+
 /**
  * Prepare the library path contract for the Python backend.
  *
@@ -31,7 +46,7 @@ export function prepareLibraryPathForPython(
     resolvedDlcDir: string,
     explicitDlcDir?: string,
 ): LibraryPathPreparation {
-    const override = (explicitDlcDir || '').trim();
+    const override = normalizeExplicitLibraryPath(explicitDlcDir);
     if (override) {
         return {
             status: 'explicit-override',
diff --git a/src/main/python.ts b/src/main/python.ts
index 0cc07ab..a3eee35 100644
--- a/src/main/python.ts
+++ b/src/main/python.ts
@@ -11,7 +11,7 @@ import * as net from 'net';
 import * as os from 'os';
 import { getActiveSoundfontPath, getDesktopConfig } from './soundfont-manager';
 import { isDebugEnabled } from './debug-log';
-import { prepareLibraryPathForPython } from './library-path-config';
+import { normalizeExplicitLibraryPath, prepareLibraryPathForPython } from './library-path-config';
 
 let pythonProcess: ChildProcess | null = null;
 // A backend that is being *gracefully* stopped (SIGTERM sent, async SIGKILL
@@ -424,8 +424,8 @@ function getPluginsDir(): string {
     return pluginsDir;
 }
 
-function getDLCDir(): string {
-    if (process.env.DLC_DIR && fs.existsSync(process.env.DLC_DIR)) return process.env.DLC_DIR;
+function getDLCDir(explicitDlcDir = normalizeExplicitLibraryPath(process.env.DLC_DIR)): string {
+    if (explicitDlcDir) return explicitDlcDir;
 
     // Read from shared config
     const configFile = path.join(getConfigDir(), 'config.json');
@@ -497,7 +497,8 @@ export async function startPython(): Promise<void> {
     }
     serverPort = await findPort(PREFERRED_PORT);
     const configDir = getConfigDir();
-    const dlcDir = getDLCDir();
+    const explicitDlcDir = normalizeExplicitLibraryPath(process.env.DLC_DIR);
+    const dlcDir = getDLCDir(explicitDlcDir);
     // Ensure the resolved library folder exists before the server starts. The
     // Python side only seeds starter content (and scans) when DLC_DIR.is_dir()
     // is true, and it can't bootstrap the folder itself (the seed's mkdir runs
@@ -514,9 +515,6 @@ export async function startPython(): Promise<void> {
     // instead. The backend re-reads that file for every scan, so a path saved in
     // Settings takes effect immediately rather than being shadowed by the
     // startup path until the Python process restarts.
-    const explicitDlcDir = process.env.DLC_DIR && fs.existsSync(process.env.DLC_DIR)
-        ? process.env.DLC_DIR
-        : undefined;
     const libraryPath = prepareLibraryPathForPython(configDir, dlcDir, explicitDlcDir);
     if (libraryPath.error) {
         console.warn(`[python] could not prepare dynamic library path (${libraryPath.status}): ${libraryPath.error}`);
diff --git a/tests/library-path-config.test.js b/tests/library-path-config.test.js
index 28e1c65..6c786fb 100644
--- a/tests/library-path-config.test.js
+++ b/tests/library-path-config.test.js
@@ -8,6 +8,7 @@ const path = require('node:path');
 const { loadTs, ROOT } = require('./_load-ts');
 
 const {
+    normalizeExplicitLibraryPath,
     prepareLibraryPathForPython,
 } = loadTs('src/main/library-path-config.ts');
 
@@ -58,19 +59,39 @@ test('an existing saved library stays config-owned and can change between scans'
 
 test('an explicit valid DLC_DIR remains an environment override', () => {
     const configDir = tmpConfigDir();
+    const managedSongs = path.join(configDir, 'Managed Songs');
+    fs.mkdirSync(managedSongs);
     const result = prepareLibraryPathForPython(
         configDir,
         'C:\\Default Songs',
-        ' D:\\Managed Songs ',
+        ` ${managedSongs} `,
     );
 
     assert.deepEqual(result, {
         status: 'explicit-override',
-        environmentDlcDir: 'D:\\Managed Songs',
+        environmentDlcDir: managedSongs,
     });
     assert.equal(fs.existsSync(path.join(configDir, 'config.json')), false);
 });
 
+test('an explicit DLC_DIR rejects whitespace, files, and missing paths', () => {
+    const root = tmpConfigDir();
+    const file = path.join(root, 'not-a-directory');
+    fs.writeFileSync(file, 'x');
+
+    assert.equal(normalizeExplicitLibraryPath('   '), undefined);
+    assert.equal(normalizeExplicitLibraryPath(file), undefined);
+    assert.equal(normalizeExplicitLibraryPath(path.join(root, 'missing')), undefined);
+});
+
+test('an explicit DLC_DIR is trimmed before directory validation', () => {
+    const root = tmpConfigDir();
+    const directory = path.join(root, 'Managed Songs');
+    fs.mkdirSync(directory);
+
+    assert.equal(normalizeExplicitLibraryPath(`  ${directory}  `), directory);
+});
+
 test('a corrupt config is never overwritten during bootstrap', () => {
     const configDir = tmpConfigDir();
     const configFile = path.join(configDir, 'config.json');
@@ -86,6 +107,8 @@ test('a corrupt config is never overwritten during bootstrap', () => {
 test('python startup does not pin its resolved fallback as DLC_DIR', () => {
     const source = fs.readFileSync(path.join(ROOT, 'src', 'main', 'python.ts'), 'utf8');
 
+    assert.match(source, /normalizeExplicitLibraryPath\(process\.env\.DLC_DIR\)/);
+    assert.doesNotMatch(source, /existsSync\(process\.env\.DLC_DIR\)/);
     assert.match(source, /prepareLibraryPathForPython\(configDir, dlcDir, explicitDlcDir\)/);
     assert.doesNotMatch(source, /DLC_DIR:\s*dlcDir/);
     assert.match(source, /delete pythonEnv\.DLC_DIR/);