diff --git a/packages/compiler-cli/src/ngtsc/typecheck/src/host.ts b/packages/compiler-cli/src/ngtsc/typecheck/src/host.ts
index 70e339b7ca3d59..2b375ab7a3f526 100644
--- a/packages/compiler-cli/src/ngtsc/typecheck/src/host.ts
+++ b/packages/compiler-cli/src/ngtsc/typecheck/src/host.ts
@@ -38,7 +38,15 @@ export class TypeCheckProgramHost implements ts.CompilerHost {
       // a cache miss.
       sf = this.delegate.getSourceFile(
           fileName, languageVersion, onError, shouldCreateNewSourceFile);
-      sf && this.sfMap.set(fileName, sf);
+      if (sf) {
+        this.sfMap.set(fileName, sf !);
+      }
+    } else if ((sf as any).redirectInfo) {
+      // When redirectInfo is provided on a sourceFile it means the same file exists in another
+      // location.
+      // We return 'redirectInfo.unredirected' to return the original file and not the, by
+      // TypeScript, suggested target file.
+      sf = (sf as any).redirectInfo.unredirected;
     }
     return sf;
   }
diff --git a/packages/compiler-cli/src/transformers/compiler_host.ts b/packages/compiler-cli/src/transformers/compiler_host.ts
index 517b974ec70561..b9bf50a87c06f8 100644
--- a/packages/compiler-cli/src/transformers/compiler_host.ts
+++ b/packages/compiler-cli/src/transformers/compiler_host.ts
@@ -440,8 +440,16 @@ export class TsCompilerAotCompilerTypeCheckHostAdapter implements ts.CompilerHos
           summary.sourceFile = ts.createSourceFile(
               fileName, summary.text, this.options.target || ts.ScriptTarget.Latest);
         }
-        sf = summary.sourceFile;
-        genFileNames = [];
+        // When redirectInfo is provided on a sourceFile it means the same file exists in another
+        // location.
+        // We return 'redirectInfo.unredirected' to return the original file and not the, by
+        // TypeScript, suggested target file.
+        if ((summary.sourceFile as any).redirectInfo) {
+          sf = (summary.sourceFile as any).redirectInfo.unredirected;
+        } else {
+          sf = summary.sourceFile;
+        }
+        if (sf) genFileNames = [];
       }
     }
     if (!sf) {
diff --git a/packages/compiler-cli/test/ngtsc/incremental_spec.ts b/packages/compiler-cli/test/ngtsc/incremental_spec.ts
index 9cf9198feb11fc..ee288769d3f054 100644
--- a/packages/compiler-cli/test/ngtsc/incremental_spec.ts
+++ b/packages/compiler-cli/test/ngtsc/incremental_spec.ts
@@ -202,6 +202,37 @@ runInEachFileSystem(() => {
       // If program reuse were configured incorrectly (as was responsible for
       // https://github.com/angular/angular/issues/30079), this would have crashed.
     });
+
+    // https://github.com/angular/angular/pull/26036
+    it('should handle redirected source files', () => {
+      env.tsconfig({fullTemplateTypeCheck: true});
+
+      // This file structure has an identical version of "a" under the root node_modules and inside
+      // of "b". Because their package.json file indicates it is the exact same version of "a",
+      // TypeScript will transform the source file of "node_modules/b/node_modules/a/index.d.ts"
+      // into a redirect to "node_modules/a/index.d.ts". During incremental compilations, we must
+      // assure not to reintroduce "node_modules/b/node_modules/a/index.d.ts" as its redirected
+      // source file, but instead use its original file.
+      env.write('node_modules/a/index.js', `export class ServiceA {}`);
+      env.write('node_modules/a/index.d.ts', `export declare class ServiceA {}`);
+      env.write('node_modules/a/package.json', `{"name": "a", "version": "1.0"}`);
+      env.write('node_modules/b/node_modules/a/index.js', `export class ServiceA {}`);
+      env.write('node_modules/b/node_modules/a/index.d.ts', `export declare class ServiceA {}`);
+      env.write('node_modules/b/node_modules/a/package.json', `{"name": "a", "version": "1.0"}`);
+      env.write('node_modules/b/index.js', `export {ServiceA as ServiceB} from 'a';`);
+      env.write('node_modules/b/index.d.ts', `export {ServiceA as ServiceB} from 'a';`);
+      env.write('test.ts', `
+        import {ServiceA} from 'a';
+        import {ServiceB} from 'b';
+      `);
+      env.driveMain();
+      env.flushWrittenFileTracking();
+
+      // Pretend a change was made to test.ts. If redirect sources were introduced into the new
+      // program, this would fail due to an assertion failure in TS.
+      env.invalidateCachedFile('test.ts');
+      env.driveMain();
+    });
   });
 
   function setupFooBarProgram(env: NgtscTestEnvironment) {
diff --git a/packages/compiler-cli/test/perform_watch_spec.ts b/packages/compiler-cli/test/perform_watch_spec.ts
index d40531418c7254..b38d732ebfd94b 100644
--- a/packages/compiler-cli/test/perform_watch_spec.ts
+++ b/packages/compiler-cli/test/perform_watch_spec.ts
@@ -107,6 +107,47 @@ describe('perform watch', () => {
     expect(getSourceFileSpy !).toHaveBeenCalledWith(utilTsPath, ts.ScriptTarget.ES5);
   });
 
+  // https://github.com/angular/angular/pull/26036
+  it('should handle redirected source files', () => {
+    const config = createConfig();
+    const host = new MockWatchHost(config);
+    host.createCompilerHost = (options: ng.CompilerOptions) => {
+      const ngHost = ng.createCompilerHost({options});
+      return ngHost;
+    };
+
+    // This file structure has an identical version of "a" under the root node_modules and inside
+    // of "b". Because their package.json file indicates it is the exact same version of "a",
+    // TypeScript will transform the source file of "node_modules/b/node_modules/a/index.d.ts"
+    // into a redirect to "node_modules/a/index.d.ts". During watch compilations, we must assure
+    // not to reintroduce "node_modules/b/node_modules/a/index.d.ts" as its redirected source file,
+    // but instead using its original file.
+    testSupport.writeFiles({
+      'node_modules/a/index.js': `export class ServiceA {}`,
+      'node_modules/a/index.d.ts': `export declare class ServiceA {}`,
+      'node_modules/a/package.json': `{"name": "a", "version": "1.0"}`,
+      'node_modules/b/node_modules/a/index.js': `export class ServiceA {}`,
+      'node_modules/b/node_modules/a/index.d.ts': `export declare class ServiceA {}`,
+      'node_modules/b/node_modules/a/package.json': `{"name": "a", "version": "1.0"}`,
+      'node_modules/b/index.js': `export {ServiceA as ServiceB} from 'a';`,
+      'node_modules/b/index.d.ts': `export {ServiceA as ServiceB} from 'a';`,
+      'src/index.ts': `
+        import {ServiceA} from 'a';
+        import {ServiceB} from 'b';
+      `,
+    });
+
+    const indexTsPath = path.posix.join(testSupport.basePath, 'src', 'index.ts');
+
+    performWatchCompilation(host);
+
+    // Trigger a file change. This recreates the program from the old program. If redirect sources
+    // were introduced into the new program, this would fail due to an assertion failure in TS.
+    host.triggerFileChange(FileChangeEvent.Change, indexTsPath);
+    expectNoDiagnostics(config.options, host.diagnostics);
+  });
+
+
   it('should recover from static analysis errors', () => {
     const config = createConfig();
     const host = new MockWatchHost(config);