diff --git a/src/cdk/drag-drop/drop-list-ref.ts b/src/cdk/drag-drop/drop-list-ref.ts
index e258bf44fff9..93e161f4b642 100644
--- a/src/cdk/drag-drop/drop-list-ref.ts
+++ b/src/cdk/drag-drop/drop-list-ref.ts
@@ -10,7 +10,7 @@ import {ElementRef, NgZone} from '@angular/core';
 import {Direction} from '@angular/cdk/bidi';
 import {coerceElement} from '@angular/cdk/coercion';
 import {ViewportRuler} from '@angular/cdk/scrolling';
-import {_supportsShadowDom} from '@angular/cdk/platform';
+import {_getShadowRoot} from '@angular/cdk/platform';
 import {Subject, Subscription, interval, animationFrameScheduler} from 'rxjs';
 import {takeUntil} from 'rxjs/operators';
 import {moveItemInArray} from './drag-utils';
@@ -907,7 +907,8 @@ export class DropListRef<T = any> {
    */
   private _getShadowRoot(): DocumentOrShadowRoot {
     if (!this._cachedShadowRoot) {
-      this._cachedShadowRoot = getShadowRoot(coerceElement(this.element)) || this._document;
+      const shadowRoot = _getShadowRoot(coerceElement(this.element)) as ShadowRoot | null;
+      this._cachedShadowRoot = shadowRoot || this._document;
     }
 
     return this._cachedShadowRoot;
@@ -1102,16 +1103,3 @@ function getElementScrollDirections(element: HTMLElement, clientRect: ClientRect
 
   return [verticalScrollDirection, horizontalScrollDirection];
 }
-
-/** Gets the shadow root of an element, if any. */
-function getShadowRoot(element: HTMLElement): DocumentOrShadowRoot | null {
-  if (_supportsShadowDom()) {
-    const rootNode = element.getRootNode ? element.getRootNode() : null;
-
-    if (rootNode instanceof ShadowRoot) {
-      return rootNode;
-    }
-  }
-
-  return null;
-}
diff --git a/src/cdk/platform/features/shadow-dom.ts b/src/cdk/platform/features/shadow-dom.ts
index 12d3ed54f969..b387fc2f5730 100644
--- a/src/cdk/platform/features/shadow-dom.ts
+++ b/src/cdk/platform/features/shadow-dom.ts
@@ -17,3 +17,16 @@ export function _supportsShadowDom(): boolean {
 
   return shadowDomIsSupported;
 }
+
+/** Gets the shadow root of an element, if supported and the element is inside the Shadow DOM. */
+export function _getShadowRoot(element: HTMLElement): Node | null {
+  if (_supportsShadowDom()) {
+    const rootNode = element.getRootNode ? element.getRootNode() : null;
+
+    if (rootNode instanceof ShadowRoot) {
+      return rootNode;
+    }
+  }
+
+  return null;
+}
diff --git a/src/material/autocomplete/autocomplete-trigger.ts b/src/material/autocomplete/autocomplete-trigger.ts
index 5818092a79ed..a7cb88cb2d13 100644
--- a/src/material/autocomplete/autocomplete-trigger.ts
+++ b/src/material/autocomplete/autocomplete-trigger.ts
@@ -17,7 +17,7 @@ import {
   ScrollStrategy,
   ConnectedPosition,
 } from '@angular/cdk/overlay';
-import {_supportsShadowDom} from '@angular/cdk/platform';
+import {_getShadowRoot} from '@angular/cdk/platform';
 import {TemplatePortal} from '@angular/cdk/portal';
 import {ViewportRuler} from '@angular/cdk/scrolling';
 import {DOCUMENT} from '@angular/common';
@@ -230,14 +230,7 @@ export class MatAutocompleteTrigger implements ControlValueAccessor, AfterViewIn
         window.addEventListener('blur', this._windowBlurHandler);
       });
 
-      if (_supportsShadowDom()) {
-        const element = this._element.nativeElement;
-        const rootNode = element.getRootNode ? element.getRootNode() : null;
-
-        // We need to take the `ShadowRoot` off of `window`, because the built-in types are
-        // incorrect. See https://github.com/Microsoft/TypeScript/issues/27929.
-        this._isInsideShadowRoot = rootNode instanceof (window as any).ShadowRoot;
-      }
+      this._isInsideShadowRoot = !!_getShadowRoot(this._element.nativeElement);
     }
   }
 
diff --git a/src/material/progress-spinner/progress-spinner.spec.ts b/src/material/progress-spinner/progress-spinner.spec.ts
index 687f4b098316..e8b6323bb792 100644
--- a/src/material/progress-spinner/progress-spinner.spec.ts
+++ b/src/material/progress-spinner/progress-spinner.spec.ts
@@ -1,9 +1,8 @@
 import {TestBed, async, inject} from '@angular/core/testing';
 import {Component, ViewEncapsulation, ViewChild, ElementRef} from '@angular/core';
 import {By} from '@angular/platform-browser';
-import {Platform} from '@angular/cdk/platform';
+import {Platform, _getShadowRoot, _supportsShadowDom} from '@angular/cdk/platform';
 import {CommonModule} from '@angular/common';
-import {_getShadowRoot} from './progress-spinner';
 import {
   MatProgressSpinnerModule,
   MatProgressSpinner,
@@ -11,8 +10,6 @@ import {
 } from './index';
 
 describe('MatProgressSpinner', () => {
-  const supportsShadowDom = typeof document.createElement('div').attachShadow !== 'undefined';
-
   beforeEach(async(() => {
     TestBed.configureTestingModule({
       imports: [MatProgressSpinnerModule, CommonModule],
@@ -357,7 +354,7 @@ describe('MatProgressSpinner', () => {
 
   it('should add the indeterminate animation style tag to the Shadow root', () => {
     // The test is only relevant in browsers that support Shadow DOM.
-    if (!supportsShadowDom) {
+    if (!_supportsShadowDom()) {
       return;
     }
 
@@ -366,7 +363,7 @@ describe('MatProgressSpinner', () => {
     fixture.detectChanges();
 
     const spinner = fixture.debugElement.query(By.css('mat-progress-spinner'))!.nativeElement;
-    const shadowRoot = _getShadowRoot(spinner, document) as HTMLElement;
+    const shadowRoot = _getShadowRoot(spinner) as HTMLElement;
 
     expect(shadowRoot.querySelector('style[mat-spinner-animation="27"]')).toBeTruthy();
 
@@ -378,7 +375,7 @@ describe('MatProgressSpinner', () => {
 
   it('should not duplicate style tags inside the Shadow root', () => {
     // The test is only relevant in browsers that support Shadow DOM.
-    if (!supportsShadowDom) {
+    if (!_supportsShadowDom()) {
       return;
     }
 
@@ -387,7 +384,7 @@ describe('MatProgressSpinner', () => {
     fixture.detectChanges();
 
     const spinner = fixture.debugElement.query(By.css('mat-progress-spinner'))!.nativeElement;
-    const shadowRoot = _getShadowRoot(spinner, document) as HTMLElement;
+    const shadowRoot = _getShadowRoot(spinner) as HTMLElement;
 
     expect(shadowRoot.querySelectorAll('style[mat-spinner-animation="39"]').length).toBe(1);
 
@@ -409,7 +406,7 @@ describe('MatProgressSpinner', () => {
   it('should add the indeterminate animation style tag to the Shadow root if the element is ' +
     'inside an ngIf', () => {
       // The test is only relevant in browsers that support Shadow DOM.
-      if (!supportsShadowDom) {
+      if (!_supportsShadowDom()) {
         return;
       }
 
@@ -418,7 +415,7 @@ describe('MatProgressSpinner', () => {
       fixture.detectChanges();
 
       const spinner = fixture.componentInstance.spinner.nativeElement;
-      const shadowRoot = _getShadowRoot(spinner, document) as HTMLElement;
+      const shadowRoot = _getShadowRoot(spinner) as HTMLElement;
 
       expect(shadowRoot.querySelector('style[mat-spinner-animation="27"]')).toBeTruthy();
 
diff --git a/src/material/progress-spinner/progress-spinner.ts b/src/material/progress-spinner/progress-spinner.ts
index 2bff6ed06786..61fe82c58299 100644
--- a/src/material/progress-spinner/progress-spinner.ts
+++ b/src/material/progress-spinner/progress-spinner.ts
@@ -7,7 +7,7 @@
  */
 
 import {coerceNumberProperty, NumberInput} from '@angular/cdk/coercion';
-import {Platform} from '@angular/cdk/platform';
+import {Platform, _getShadowRoot} from '@angular/cdk/platform';
 import {DOCUMENT} from '@angular/common';
 import {
   ChangeDetectionStrategy,
@@ -218,7 +218,7 @@ export class MatProgressSpinner extends _MatProgressSpinnerMixinBase implements
     // Note that we need to look up the root node in ngOnInit, rather than the constructor, because
     // Angular seems to create the element outside the shadow root and then moves it inside, if the
     // node is inside an `ngIf` and a ShadowDom-encapsulated component.
-    this._styleRoot = _getShadowRoot(element, this._document) || this._document.head;
+    this._styleRoot = _getShadowRoot(element) || this._document.head;
     this._attachStyleNode();
 
     // On IE and Edge, we can't animate the `stroke-dashoffset`
@@ -333,26 +333,3 @@ export class MatSpinner extends MatProgressSpinner {
     this.mode = 'indeterminate';
   }
 }
-
-
-/** Gets the shadow root of an element, if supported and the element is inside the Shadow DOM. */
-export function _getShadowRoot(element: HTMLElement, _document: Document): Node | null {
-  // TODO(crisbeto): see whether we should move this into the CDK
-  // feature detection utilities once #15616 gets merged in.
-  if (typeof window !== 'undefined') {
-    const head = _document.head;
-
-    // Check whether the browser supports Shadow DOM.
-    if (head && ((head as any).createShadowRoot || head.attachShadow)) {
-      const rootNode = element.getRootNode ? element.getRootNode() : null;
-
-      // We need to take the `ShadowRoot` off of `window`, because the built-in types are
-      // incorrect. See https://github.com/Microsoft/TypeScript/issues/27929.
-      if (rootNode instanceof (window as any).ShadowRoot) {
-        return rootNode;
-      }
-    }
-  }
-
-  return null;
-}
diff --git a/tools/public_api_guard/cdk/platform.d.ts b/tools/public_api_guard/cdk/platform.d.ts
index 2b42a5ace81d..d5926f5f4345 100644
--- a/tools/public_api_guard/cdk/platform.d.ts
+++ b/tools/public_api_guard/cdk/platform.d.ts
@@ -1,3 +1,5 @@
+export declare function _getShadowRoot(element: HTMLElement): Node | null;
+
 export declare function _supportsShadowDom(): boolean;
 
 export declare function getRtlScrollAxisType(): RtlScrollAxisType;