diff --git a/src/loaders/less/import-plugin.ts b/src/loaders/less/import-plugin.ts
index 54b90659..a4d24612 100644
--- a/src/loaders/less/import-plugin.ts
+++ b/src/loaders/less/import-plugin.ts
@@ -1,13 +1,11 @@
 import fs from "fs-extra";
-import { LoadedFile, Plugin, Less } from "less";
+import { LoadedFile, Plugin, FileManagerInterface, Less } from "less";
 import resolveAsync from "../../utils/resolve-async";
 import { moduleRe, getUrlOfPartial } from "../../utils/resolve-utils";
 
-// eslint-disable-next-line @typescript-eslint/explicit-function-return-type
-const getManager = () => {
+const getStylesFileManager = (): FileManagerInterface => {
   const less = require("less") as Less;
-
-  class StylesFileManager extends less.FileManager {
+  return new (class extends less.AbstractFileManager implements FileManagerInterface {
     supports(): boolean {
       return true;
     }
@@ -16,50 +14,47 @@ const getManager = () => {
       return false;
     }
 
-    async loadFile(filename: string, currentDirectory: string): Promise<LoadedFile> {
-      const options = { basedir: currentDirectory, extensions: [".less", ".css"] };
+    async loadFile(filename: string, basedir: string): Promise<LoadedFile> {
+      const options = { basedir, extensions: [".less", ".css"] };
+      let id: string;
 
       if (!moduleRe.test(filename)) {
-        let resolved: string;
         try {
           // Give precedence to importing a partial
           try {
-            resolved = await resolveAsync(getUrlOfPartial(filename), options);
+            id = await resolveAsync(getUrlOfPartial(filename), options);
           } catch (error) {
-            resolved = await resolveAsync(filename, options);
+            id = await resolveAsync(filename, options);
           }
         } catch (error) {
           // Give precedence to importing a partial
           try {
-            resolved = await resolveAsync(`./${getUrlOfPartial(filename)}`, options);
+            id = await resolveAsync(`./${getUrlOfPartial(filename)}`, options);
           } catch (error) {
-            resolved = await resolveAsync(`./${filename}`, options);
+            id = await resolveAsync(`./${filename}`, options);
           }
         }
-        return { filename: resolved, contents: await fs.readFile(resolved, "utf8") };
+        return { filename: id, contents: await fs.readFile(id, "utf8") };
       }
 
       const moduleUrl = filename.slice(1);
       const partialUrl = getUrlOfPartial(moduleUrl);
 
       // Give precedence to importing a partial
-      let resolved: string;
       try {
-        resolved = await resolveAsync(partialUrl, options);
+        id = await resolveAsync(partialUrl, options);
       } catch (error) {
-        resolved = await resolveAsync(moduleUrl, options);
+        id = await resolveAsync(moduleUrl, options);
       }
 
-      return { filename: resolved, contents: await fs.readFile(resolved, "utf8") };
+      return { filename: id, contents: await fs.readFile(id, "utf8") };
     }
-  }
-
-  return new StylesFileManager();
+  })();
 };
 
 const importPlugin: Plugin = {
   install(_, pluginManager) {
-    pluginManager.addFileManager(getManager());
+    pluginManager.addFileManager(getStylesFileManager());
   },
 };
 
diff --git a/src/typings/less.d.ts b/src/typings/less.d.ts
index aeda9b42..7c8e8814 100644
--- a/src/typings/less.d.ts
+++ b/src/typings/less.d.ts
@@ -4,7 +4,7 @@ declare module "less" {
     filename: string;
     relativeUrls: boolean;
     rootpath: string;
-    currentDirectory: string;
+    currentDir: string;
     entryPath: string;
     rootFilename: string;
     reference: boolean;
@@ -34,18 +34,30 @@ declare module "less" {
 
   export type LoadOptions = { [k: string]: unknown };
 
-  class AbstractFileManager {}
-  class FileManager extends AbstractFileManager {
-    supports(filename: string, currentDirectory: string, options: LoadOptions): boolean;
-    supportsSync(filename: string, currentDirectory: string, options: LoadOptions): boolean;
-    loadFile(filename: string, currentDirectory: string, options: LoadOptions): Promise<LoadedFile>;
-    loadFileSync(filename: string, currentDirectory: string, options: LoadOptions): LoadedFileSync;
+  export interface AbstractFileManagerInterface {
+    supportsSync(filename: string, currentDir: string, options: LoadOptions): boolean;
+  }
+
+  export interface FileManagerInterface extends AbstractFileManagerInterface {
+    supports(filename: string, currentDir: string, options: LoadOptions): boolean;
+    loadFile(filename: string, currentDir: string, options: LoadOptions): Promise<LoadedFile>;
+    loadFileSync?(filename: string, currentDir: string, options: LoadOptions): LoadedFileSync;
+  }
+
+  class AbstractFileManager implements AbstractFileManagerInterface {
+    supportsSync(filename: string, currentDir: string, options: LoadOptions): boolean;
+  }
+
+  class FileManager extends AbstractFileManager implements FileManagerInterface {
+    supports(filename: string, currentDir: string, options: LoadOptions): boolean;
+    loadFile(filename: string, currentDir: string, options: LoadOptions): Promise<LoadedFile>;
+    loadFileSync?(filename: string, currentDir: string, options: LoadOptions): LoadedFileSync;
   }
 
   class PluginManager {
     constructor(less: Less);
     addPreProcessor(preProcessor: PreProcessor, priority?: number): void;
-    addFileManager(fileManager: FileManager): void;
+    addFileManager(fileManager: FileManagerInterface): void;
   }
 
   export interface Plugin {
@@ -113,6 +125,7 @@ declare module "less" {
     sheets: HTMLLinkElement[];
     version: number[];
 
+    AbstractFileManager: typeof AbstractFileManager;
     FileManager: typeof FileManager;
 
     render(input: string, callback: RenderCallback): void;