diff --git a/packages/compiler-cli/ngcc/src/utils.ts b/packages/compiler-cli/ngcc/src/utils.ts
index f729abe386..acd7ea69fa 100644
--- a/packages/compiler-cli/ngcc/src/utils.ts
+++ b/packages/compiler-cli/ngcc/src/utils.ts
@@ -7,7 +7,7 @@
  */
 import * as ts from 'typescript';
 
-import {absoluteFrom, AbsoluteFsPath, FileSystem} from '../../src/ngtsc/file_system';
+import {absoluteFrom, AbsoluteFsPath, FileSystem, isRooted} from '../../src/ngtsc/file_system';
 import {KnownDeclaration} from '../../src/ngtsc/reflection';
 
 /**
@@ -85,10 +85,11 @@ export type PathMappings = {
 /**
  * Test whether a path is "relative".
  *
- * Relative paths start with `/`, `./` or `../`; or are simply `.` or `..`.
+ * Relative paths start with `/`, `./` or `../` (or the Windows equivalents); or are simply `.` or
+ * `..`.
  */
 export function isRelativePath(path: string): boolean {
-  return /^\/|^\.\.?($|\/)/.test(path);
+  return isRooted(path) || /^\.\.?(\/|\\|$)/.test(path);
 }
 
 /**
diff --git a/packages/compiler-cli/ngcc/test/dependencies/module_resolver_spec.ts b/packages/compiler-cli/ngcc/test/dependencies/module_resolver_spec.ts
index 2ef140ca71..503c157161 100644
--- a/packages/compiler-cli/ngcc/test/dependencies/module_resolver_spec.ts
+++ b/packages/compiler-cli/ngcc/test/dependencies/module_resolver_spec.ts
@@ -67,16 +67,29 @@ runInEachFileSystem(() => {
       ]);
     });
 
-    describe('resolveModule()', () => {
+    describe('resolveModuleImport()', () => {
       describe('with relative paths', () => {
         it('should resolve sibling, child and aunt modules', () => {
           const resolver = new ModuleResolver(getFileSystem());
+
+          // With relative file paths.
           expect(resolver.resolveModuleImport('./x', _('/libs/local-package/index.js')))
               .toEqual(new ResolvedRelativeModule(_('/libs/local-package/x.js')));
           expect(resolver.resolveModuleImport('./sub-folder', _('/libs/local-package/index.js')))
               .toEqual(new ResolvedRelativeModule(_('/libs/local-package/sub-folder/index.js')));
           expect(resolver.resolveModuleImport('../x', _('/libs/local-package/sub-folder/index.js')))
               .toEqual(new ResolvedRelativeModule(_('/libs/local-package/x.js')));
+
+          // With absolute file paths.
+          expect(resolver.resolveModuleImport(
+                     _('/libs/local-package/x'), _('/libs/local-package/index.js')))
+              .toEqual(new ResolvedRelativeModule(_('/libs/local-package/x.js')));
+          expect(resolver.resolveModuleImport(
+                     _('/libs/local-package/sub-folder'), _('/libs/local-package/index.js')))
+              .toEqual(new ResolvedRelativeModule(_('/libs/local-package/sub-folder/index.js')));
+          expect(resolver.resolveModuleImport(
+                     _('/libs/local-package/x'), _('/libs/local-package/sub-folder/index.js')))
+              .toEqual(new ResolvedRelativeModule(_('/libs/local-package/x.js')));
         });
 
         it('should return `null` if the resolved module relative module does not exist', () => {
diff --git a/packages/compiler-cli/ngcc/test/utils_spec.ts b/packages/compiler-cli/ngcc/test/utils_spec.ts
index f373e5313a..d01b1e3e9a 100644
--- a/packages/compiler-cli/ngcc/test/utils_spec.ts
+++ b/packages/compiler-cli/ngcc/test/utils_spec.ts
@@ -7,6 +7,8 @@
  */
 
 import * as ts from 'typescript';
+import {absoluteFrom as _abs} from '../../src/ngtsc/file_system';
+import {runInEachFileSystem} from '../../src/ngtsc/file_system/testing';
 import {KnownDeclaration} from '../../src/ngtsc/reflection';
 import {FactoryMap, getTsHelperFnFromDeclaration, getTsHelperFnFromIdentifier, isRelativePath, stripExtension} from '../src/utils';
 
@@ -167,30 +169,36 @@ describe('getTsHelperFnFromIdentifier()', () => {
   });
 });
 
-describe('isRelativePath()', () => {
-  it('should return true for relative paths', () => {
-    expect(isRelativePath('.')).toBe(true);
-    expect(isRelativePath('..')).toBe(true);
-    expect(isRelativePath('./')).toBe(true);
-    expect(isRelativePath('../')).toBe(true);
-    expect(isRelativePath('./abc/xyz')).toBe(true);
-    expect(isRelativePath('../abc/xyz')).toBe(true);
-  });
+runInEachFileSystem(() => {
+  describe('isRelativePath()', () => {
+    it('should return true for relative paths', () => {
+      expect(isRelativePath('.')).toBe(true);
+      expect(isRelativePath('..')).toBe(true);
+      expect(isRelativePath('./')).toBe(true);
+      expect(isRelativePath('.\\')).toBe(true);
+      expect(isRelativePath('../')).toBe(true);
+      expect(isRelativePath('..\\')).toBe(true);
+      expect(isRelativePath('./abc/xyz')).toBe(true);
+      expect(isRelativePath('.\\abc\\xyz')).toBe(true);
+      expect(isRelativePath('../abc/xyz')).toBe(true);
+      expect(isRelativePath('..\\abc\\xyz')).toBe(true);
+    });
 
-  it('should return true for absolute paths', () => {
-    expect(isRelativePath('/')).toBe(true);
-    expect(isRelativePath('/abc/xyz')).toBe(true);
-  });
+    it('should return true for absolute paths', () => {
+      expect(isRelativePath(_abs('/'))).toBe(true);
+      expect(isRelativePath(_abs('/abc/xyz'))).toBe(true);
+    });
 
-  it('should return false for other paths', () => {
-    expect(isRelativePath('abc')).toBe(false);
-    expect(isRelativePath('abc/xyz')).toBe(false);
-    expect(isRelativePath('.abc')).toBe(false);
-    expect(isRelativePath('..abc')).toBe(false);
-    expect(isRelativePath('@abc')).toBe(false);
-    expect(isRelativePath('.abc/xyz')).toBe(false);
-    expect(isRelativePath('..abc/xyz')).toBe(false);
-    expect(isRelativePath('@abc/xyz')).toBe(false);
+    it('should return false for other paths', () => {
+      expect(isRelativePath('abc')).toBe(false);
+      expect(isRelativePath('abc/xyz')).toBe(false);
+      expect(isRelativePath('.abc')).toBe(false);
+      expect(isRelativePath('..abc')).toBe(false);
+      expect(isRelativePath('@abc')).toBe(false);
+      expect(isRelativePath('.abc/xyz')).toBe(false);
+      expect(isRelativePath('..abc/xyz')).toBe(false);
+      expect(isRelativePath('@abc/xyz')).toBe(false);
+    });
   });
 });
 
diff --git a/packages/compiler-cli/src/ngtsc/file_system/index.ts b/packages/compiler-cli/src/ngtsc/file_system/index.ts
index 594af21923..2bf3079757 100644
--- a/packages/compiler-cli/src/ngtsc/file_system/index.ts
+++ b/packages/compiler-cli/src/ngtsc/file_system/index.ts
@@ -7,7 +7,7 @@
  */
 export {CachedFileSystem} from './src/cached_file_system';
 export {NgtscCompilerHost} from './src/compiler_host';
-export {absoluteFrom, absoluteFromSourceFile, basename, dirname, getFileSystem, isRoot, join, relative, relativeFrom, resolve, setFileSystem} from './src/helpers';
+export {absoluteFrom, absoluteFromSourceFile, basename, dirname, getFileSystem, isRoot, isRooted, join, relative, relativeFrom, resolve, setFileSystem} from './src/helpers';
 export {LogicalFileSystem, LogicalProjectPath} from './src/logical';
 export {NodeJSFileSystem} from './src/node_js_file_system';
 export {AbsoluteFsPath, FileStats, FileSystem, PathSegment, PathString} from './src/types';
diff --git a/packages/compiler-cli/src/ngtsc/file_system/src/helpers.ts b/packages/compiler-cli/src/ngtsc/file_system/src/helpers.ts
index 9cf87fedb6..61d676e058 100644
--- a/packages/compiler-cli/src/ngtsc/file_system/src/helpers.ts
+++ b/packages/compiler-cli/src/ngtsc/file_system/src/helpers.ts
@@ -37,8 +37,8 @@ export function absoluteFromSourceFile(sf: ts.SourceFile): AbsoluteFsPath {
 }
 
 /**
-* Convert the path `path` to a `PathSegment`, throwing an error if it's not a relative path.
-*/
+ * Convert the path `path` to a `PathSegment`, throwing an error if it's not a relative path.
+ */
 export function relativeFrom(path: string): PathSegment {
   const normalized = normalizeSeparators(path);
   if (fs.isRooted(normalized)) {
@@ -73,6 +73,13 @@ export function isRoot(path: AbsoluteFsPath): boolean {
   return fs.isRoot(path);
 }
 
+/**
+ * Static access to `isRooted`.
+ */
+export function isRooted(path: string): boolean {
+  return fs.isRooted(path);
+}
+
 /**
  * Static access to `relative`.
  */