diff --git a/integration/ngcc/test.sh b/integration/ngcc/test.sh
index b545def610..e17972a122 100755
--- a/integration/ngcc/test.sh
+++ b/integration/ngcc/test.sh
@@ -125,6 +125,21 @@ assertSucceeded "Expected 'ngcc' to log 'Compiling'."
   assertSucceeded "Expected '@angular/cdk/a11y' (umd) to actually have decorators via static properties."
 
 
+# Did it transform imports in UMD correctly?
+# (E.g. no trailing commas, so that it remains compatible with legacy browsers, such as IE11.)
+  grep "factory(exports, require('rxjs'), require('rxjs/operators'))" node_modules/@angular/core/bundles/core.umd.js
+  assertSucceeded "Expected 'ngcc' to not add trailing commas to CommonJS block in UMD."
+
+  grep "define('@angular/core', \['exports', 'rxjs', 'rxjs/operators'], factory)" node_modules/@angular/core/bundles/core.umd.js
+  assertSucceeded "Expected 'ngcc' to not add trailing commas to AMD block in UMD."
+
+  grep "factory((global.ng = global.ng || {}, global.ng.core = {}), global.rxjs, global.rxjs.operators)" node_modules/@angular/core/bundles/core.umd.js
+  assertSucceeded "Expected 'ngcc' to not add trailing commas to globals block in UMD."
+
+  grep "(this, (function (exports, rxjs, operators) {" node_modules/@angular/core/bundles/core.umd.js
+  assertSucceeded "Expected 'ngcc' to not add trailing commas to factory function parameters in UMD."
+
+
 # Can it be safely run again (as a noop)?
 # And check that it logged skipping compilation as expected
 ngcc -l debug | grep 'Skipping'
diff --git a/packages/compiler-cli/ngcc/src/rendering/commonjs_rendering_formatter.ts b/packages/compiler-cli/ngcc/src/rendering/commonjs_rendering_formatter.ts
index 65200cb991..30938fc5ac 100644
--- a/packages/compiler-cli/ngcc/src/rendering/commonjs_rendering_formatter.ts
+++ b/packages/compiler-cli/ngcc/src/rendering/commonjs_rendering_formatter.ts
@@ -30,6 +30,11 @@ export class CommonJsRenderingFormatter extends Esm5RenderingFormatter {
    *  Add the imports below any in situ imports as `require` calls.
    */
   addImports(output: MagicString, imports: Import[], file: ts.SourceFile): void {
+    // Avoid unnecessary work if there are no imports to add.
+    if (imports.length === 0) {
+      return;
+    }
+
     const insertionPoint = this.findEndOfImports(file);
     const renderedImports =
         imports.map(i => `var ${i.qualifier} = require('${i.specifier}');\n`).join('');
diff --git a/packages/compiler-cli/ngcc/src/rendering/esm_rendering_formatter.ts b/packages/compiler-cli/ngcc/src/rendering/esm_rendering_formatter.ts
index 54e46f63fb..98a35134e2 100644
--- a/packages/compiler-cli/ngcc/src/rendering/esm_rendering_formatter.ts
+++ b/packages/compiler-cli/ngcc/src/rendering/esm_rendering_formatter.ts
@@ -32,6 +32,10 @@ export class EsmRenderingFormatter implements RenderingFormatter {
    *  Add the imports at the top of the file, after any imports that are already there.
    */
   addImports(output: MagicString, imports: Import[], sf: ts.SourceFile): void {
+    if (imports.length === 0) {
+      return;
+    }
+
     const insertionPoint = this.findEndOfImports(sf);
     const renderedImports =
         imports.map(i => `import * as ${i.qualifier} from '${i.specifier}';\n`).join('');
@@ -294,4 +298,4 @@ function getEndExceptSemicolon(statement: ts.Statement): number {
   const lastToken = statement.getLastToken();
   return (lastToken && lastToken.kind === ts.SyntaxKind.SemicolonToken) ? statement.getEnd() - 1 :
                                                                           statement.getEnd();
-}
\ No newline at end of file
+}
diff --git a/packages/compiler-cli/ngcc/src/rendering/umd_rendering_formatter.ts b/packages/compiler-cli/ngcc/src/rendering/umd_rendering_formatter.ts
index 0b3dc215c8..2319171bce 100644
--- a/packages/compiler-cli/ngcc/src/rendering/umd_rendering_formatter.ts
+++ b/packages/compiler-cli/ngcc/src/rendering/umd_rendering_formatter.ts
@@ -30,6 +30,10 @@ export class UmdRenderingFormatter extends Esm5RenderingFormatter {
    *  Add the imports to the UMD module IIFE.
    */
   addImports(output: MagicString, imports: Import[], file: ts.SourceFile): void {
+    if (imports.length === 0) {
+      return;
+    }
+
     // Assume there is only one UMD module in the file
     const umdModule = this.umdHost.getUmdModule(file);
     if (!umdModule) {
diff --git a/packages/compiler-cli/ngcc/test/rendering/commonjs_rendering_formatter_spec.ts b/packages/compiler-cli/ngcc/test/rendering/commonjs_rendering_formatter_spec.ts
index 30a1390a6c..ad96ba569b 100644
--- a/packages/compiler-cli/ngcc/test/rendering/commonjs_rendering_formatter_spec.ts
+++ b/packages/compiler-cli/ngcc/test/rendering/commonjs_rendering_formatter_spec.ts
@@ -187,6 +187,17 @@ var core = require('@angular/core');
 var i0 = require('@angular/core');
 var i1 = require('@angular/common');`);
       });
+
+      it('should leave the file unchanged if there are no imports to add', () => {
+        const {renderer, sourceFile} = setup(PROGRAM);
+        const output = new MagicString(PROGRAM.contents);
+        const contentsBefore = output.toString();
+
+        renderer.addImports(output, [], sourceFile);
+        const contentsAfter = output.toString();
+
+        expect(contentsAfter).toBe(contentsBefore);
+      });
     });
 
     describe('addExports', () => {
diff --git a/packages/compiler-cli/ngcc/test/rendering/esm5_rendering_formatter_spec.ts b/packages/compiler-cli/ngcc/test/rendering/esm5_rendering_formatter_spec.ts
index 79701f3378..d98f4d73cc 100644
--- a/packages/compiler-cli/ngcc/test/rendering/esm5_rendering_formatter_spec.ts
+++ b/packages/compiler-cli/ngcc/test/rendering/esm5_rendering_formatter_spec.ts
@@ -195,6 +195,17 @@ import {Directive} from '@angular/core';
 import * as i0 from '@angular/core';
 import * as i1 from '@angular/common';`);
       });
+
+      it('should leave the file unchanged if there are no imports to add', () => {
+        const {renderer, sourceFile} = setup(PROGRAM);
+        const output = new MagicString(PROGRAM.contents);
+        const contentsBefore = output.toString();
+
+        renderer.addImports(output, [], sourceFile);
+        const contentsAfter = output.toString();
+
+        expect(contentsAfter).toBe(contentsBefore);
+      });
     });
 
     describe('addExports', () => {
diff --git a/packages/compiler-cli/ngcc/test/rendering/esm_rendering_formatter_spec.ts b/packages/compiler-cli/ngcc/test/rendering/esm_rendering_formatter_spec.ts
index 2336cd742e..85d43e230f 100644
--- a/packages/compiler-cli/ngcc/test/rendering/esm_rendering_formatter_spec.ts
+++ b/packages/compiler-cli/ngcc/test/rendering/esm_rendering_formatter_spec.ts
@@ -112,6 +112,17 @@ import {Directive} from '@angular/core';
 import * as i0 from '@angular/core';
 import * as i1 from '@angular/common';`);
       });
+
+      it('should leave the file unchanged if there are no imports to add', () => {
+        const {renderer, sourceFile} = setup([PROGRAM]);
+        const output = new MagicString(PROGRAM.contents);
+        const contentsBefore = output.toString();
+
+        renderer.addImports(output, [], sourceFile);
+        const contentsAfter = output.toString();
+
+        expect(contentsAfter).toBe(contentsBefore);
+      });
     });
 
     describe('addExports', () => {
diff --git a/packages/compiler-cli/ngcc/test/rendering/umd_rendering_formatter_spec.ts b/packages/compiler-cli/ngcc/test/rendering/umd_rendering_formatter_spec.ts
index 0a0a8bc665..07f3e11420 100644
--- a/packages/compiler-cli/ngcc/test/rendering/umd_rendering_formatter_spec.ts
+++ b/packages/compiler-cli/ngcc/test/rendering/umd_rendering_formatter_spec.ts
@@ -325,6 +325,18 @@ typeof define === 'function' && define.amd ? define('file', ['exports','/tslib',
         expect(outputSrc).toContain(`(factory(global.ng.core,global.ng.common));`);
         expect(outputSrc).toContain(`(function (i0,i1) {'use strict';`);
       });
+
+      it('should leave the file unchanged if there are no imports to add', () => {
+        const {renderer, program} = setup(PROGRAM);
+        const file = getSourceFileOrError(program, _('/node_modules/test-package/some/file.js'));
+        const output = new MagicString(PROGRAM.contents);
+        const contentsBefore = output.toString();
+
+        renderer.addImports(output, [], file);
+        const contentsAfter = output.toString();
+
+        expect(contentsAfter).toBe(contentsBefore);
+      });
     });
 
     describe('addExports', () => {