diff --git a/packages/compiler-cli/src/ngtsc/file_system/src/cached_file_system.ts b/packages/compiler-cli/src/ngtsc/file_system/src/cached_file_system.ts
index a141dc5550..7b083ab7c1 100644
--- a/packages/compiler-cli/src/ngtsc/file_system/src/cached_file_system.ts
+++ b/packages/compiler-cli/src/ngtsc/file_system/src/cached_file_system.ts
@@ -74,11 +74,6 @@ export class CachedFileSystem implements FileSystem {
     this.existsCache.set(to, true);
   }
 
-  mkdir(path: AbsoluteFsPath): void {
-    this.delegate.mkdir(path);
-    this.existsCache.set(path, true);
-  }
-
   ensureDir(path: AbsoluteFsPath): void {
     this.delegate.ensureDir(path);
     while (!this.isRoot(path)) {
diff --git a/packages/compiler-cli/src/ngtsc/file_system/src/invalid_file_system.ts b/packages/compiler-cli/src/ngtsc/file_system/src/invalid_file_system.ts
index 86023671a7..fcc7cc2034 100644
--- a/packages/compiler-cli/src/ngtsc/file_system/src/invalid_file_system.ts
+++ b/packages/compiler-cli/src/ngtsc/file_system/src/invalid_file_system.ts
@@ -27,7 +27,6 @@ export class InvalidFileSystem implements FileSystem {
   extname(path: AbsoluteFsPath|PathSegment): string { throw makeError(); }
   copyFile(from: AbsoluteFsPath, to: AbsoluteFsPath): void { throw makeError(); }
   moveFile(from: AbsoluteFsPath, to: AbsoluteFsPath): void { throw makeError(); }
-  mkdir(path: AbsoluteFsPath): void { throw makeError(); }
   ensureDir(path: AbsoluteFsPath): void { throw makeError(); }
   isCaseSensitive(): boolean { throw makeError(); }
   resolve(...paths: string[]): AbsoluteFsPath { throw makeError(); }
diff --git a/packages/compiler-cli/src/ngtsc/file_system/src/node_js_file_system.ts b/packages/compiler-cli/src/ngtsc/file_system/src/node_js_file_system.ts
index 627a75d5d2..940afcb2cf 100644
--- a/packages/compiler-cli/src/ngtsc/file_system/src/node_js_file_system.ts
+++ b/packages/compiler-cli/src/ngtsc/file_system/src/node_js_file_system.ts
@@ -28,7 +28,6 @@ export class NodeJSFileSystem implements FileSystem {
   pwd(): AbsoluteFsPath { return this.normalize(process.cwd()) as AbsoluteFsPath; }
   copyFile(from: AbsoluteFsPath, to: AbsoluteFsPath): void { fs.copyFileSync(from, to); }
   moveFile(from: AbsoluteFsPath, to: AbsoluteFsPath): void { fs.renameSync(from, to); }
-  mkdir(path: AbsoluteFsPath): void { fs.mkdirSync(path); }
   ensureDir(path: AbsoluteFsPath): void {
     const parents: AbsoluteFsPath[] = [];
     while (!this.isRoot(path) && !this.exists(path)) {
@@ -73,7 +72,7 @@ export class NodeJSFileSystem implements FileSystem {
 
   private safeMkdir(path: AbsoluteFsPath): void {
     try {
-      this.mkdir(path);
+      fs.mkdirSync(path);
     } catch (err) {
       // Ignore the error, if the path already exists and points to a directory.
       // Re-throw otherwise.
diff --git a/packages/compiler-cli/src/ngtsc/file_system/src/types.ts b/packages/compiler-cli/src/ngtsc/file_system/src/types.ts
index 40cf6a6f87..a037459f1a 100644
--- a/packages/compiler-cli/src/ngtsc/file_system/src/types.ts
+++ b/packages/compiler-cli/src/ngtsc/file_system/src/types.ts
@@ -46,7 +46,6 @@ export interface FileSystem {
   extname(path: AbsoluteFsPath|PathSegment): string;
   copyFile(from: AbsoluteFsPath, to: AbsoluteFsPath): void;
   moveFile(from: AbsoluteFsPath, to: AbsoluteFsPath): void;
-  mkdir(path: AbsoluteFsPath): void;
   ensureDir(path: AbsoluteFsPath): void;
   isCaseSensitive(): boolean;
   isRoot(path: AbsoluteFsPath): boolean;
diff --git a/packages/compiler-cli/src/ngtsc/file_system/test/cached_file_system_spec.ts b/packages/compiler-cli/src/ngtsc/file_system/test/cached_file_system_spec.ts
index 9bf2a7ccfa..d817045c57 100644
--- a/packages/compiler-cli/src/ngtsc/file_system/test/cached_file_system_spec.ts
+++ b/packages/compiler-cli/src/ngtsc/file_system/test/cached_file_system_spec.ts
@@ -234,22 +234,6 @@ describe('CachedFileSystem', () => {
     });
   });
 
-  describe('mkdir()', () => {
-    it('should call delegate', () => {
-      const spy = spyOn(delegate, 'mkdir');
-      fs.mkdir(xyzPath);
-      expect(spy).toHaveBeenCalledWith(xyzPath);
-    });
-
-    it('should update the "exists" cache', () => {
-      spyOn(delegate, 'mkdir');
-      const existsSpy = spyOn(delegate, 'exists');
-      fs.mkdir(xyzPath);
-      expect(fs.exists(xyzPath)).toEqual(true);
-      expect(existsSpy).not.toHaveBeenCalled();
-    });
-  });
-
   describe('ensureDir()', () => {
     it('should call delegate', () => {
       const ensureDirSpy = spyOn(delegate, 'ensureDir');
diff --git a/packages/compiler-cli/src/ngtsc/file_system/test/node_js_file_system_spec.ts b/packages/compiler-cli/src/ngtsc/file_system/test/node_js_file_system_spec.ts
index b1e6109cd0..34fe48dfd6 100644
--- a/packages/compiler-cli/src/ngtsc/file_system/test/node_js_file_system_spec.ts
+++ b/packages/compiler-cli/src/ngtsc/file_system/test/node_js_file_system_spec.ts
@@ -105,14 +105,6 @@ describe('NodeJSFileSystem', () => {
     });
   });
 
-  describe('mkdir()', () => {
-    it('should delegate to fs.mkdirSync()', () => {
-      const spy = spyOn(realFs, 'mkdirSync');
-      fs.mkdir(xyzPath);
-      expect(spy).toHaveBeenCalledWith(xyzPath);
-    });
-  });
-
   describe('ensureDir()', () => {
     it('should call exists() and fs.mkdir()', () => {
       const aPath = absoluteFrom('/a');
diff --git a/packages/compiler-cli/src/ngtsc/file_system/testing/src/mock_file_system.ts b/packages/compiler-cli/src/ngtsc/file_system/testing/src/mock_file_system.ts
index a19aa08eab..5f7cbbbe71 100644
--- a/packages/compiler-cli/src/ngtsc/file_system/testing/src/mock_file_system.ts
+++ b/packages/compiler-cli/src/ngtsc/file_system/testing/src/mock_file_system.ts
@@ -96,10 +96,21 @@ export abstract class MockFileSystem implements FileSystem {
     delete folder[name];
   }
 
-  mkdir(path: AbsoluteFsPath): void { this.ensureFolders(this._fileTree, this.splitPath(path)); }
-
   ensureDir(path: AbsoluteFsPath): void {
-    this.ensureFolders(this._fileTree, this.splitPath(path));
+    const segments = this.splitPath(path);
+    let current: Folder = this._fileTree;
+
+    // Convert the root folder to a canonical empty string `''` (on Windows it would be `'C:'`).
+    segments[0] = '';
+    for (const segment of segments) {
+      if (isFile(current[segment])) {
+        throw new Error(`Folder already exists as a file.`);
+      }
+      if (!current[segment]) {
+        current[segment] = {};
+      }
+      current = current[segment] as Folder;
+    }
   }
 
   isRoot(path: AbsoluteFsPath): boolean { return this.dirname(path) === path; }
@@ -173,21 +184,6 @@ export abstract class MockFileSystem implements FileSystem {
     const file = segments.pop() !;
     return [path.substring(0, path.length - file.length - 1) as AbsoluteFsPath, file];
   }
-
-  protected ensureFolders(current: Folder, segments: string[]): Folder {
-    // Convert the root folder to a canonical empty string `""` (on Windows it would be `C:`).
-    segments[0] = '';
-    for (const segment of segments) {
-      if (isFile(current[segment])) {
-        throw new Error(`Folder already exists as a file.`);
-      }
-      if (!current[segment]) {
-        current[segment] = {};
-      }
-      current = current[segment] as Folder;
-    }
-    return current;
-  }
 }
 export interface FindResult {
   path: AbsoluteFsPath;