diff --git a/packages/compiler-cli/ngcc/src/host/esm2015_host.ts b/packages/compiler-cli/ngcc/src/host/esm2015_host.ts
index 5a14f1cd5f860..58bbdff8e5203 100644
--- a/packages/compiler-cli/ngcc/src/host/esm2015_host.ts
+++ b/packages/compiler-cli/ngcc/src/host/esm2015_host.ts
@@ -344,10 +344,18 @@ export class Esm2015ReflectionHost extends TypeScriptReflectionHost implements N
     return superDeclaration;
   }
 
-  /** Gets all decorators of the given class symbol. */
+  /**
+   * Gets all decorators of the given class symbol. Any decorator that have been synthetically
+   * injected by a migration will not be present in the returned collection.
+   */
   getDecoratorsOfSymbol(symbol: NgccClassSymbol): Decorator[]|null {
     const {classDecorators} = this.acquireDecoratorInfo(symbol);
-    return classDecorators;
+    if (classDecorators === null) {
+      return null;
+    }
+
+    // Return a clone of the array to prevent consumers from mutating the cache.
+    return Array.from(classDecorators);
   }
 
   /**
diff --git a/packages/compiler-cli/ngcc/test/host/esm2015_host_spec.ts b/packages/compiler-cli/ngcc/test/host/esm2015_host_spec.ts
index d85f29e9beec7..c29afece754e9 100644
--- a/packages/compiler-cli/ngcc/test/host/esm2015_host_spec.ts
+++ b/packages/compiler-cli/ngcc/test/host/esm2015_host_spec.ts
@@ -1931,6 +1931,20 @@ runInEachFileSystem(() => {
         expect(classDecoratorsSecondary.length).toEqual(1);
         expect(classDecoratorsSecondary[0] !.map(d => d.name)).toEqual(['Directive']);
       });
+
+      it('should return a cloned array on each invocation', () => {
+        loadTestFiles(DECORATED_FILES);
+        const {program} = makeTestBundleProgram(getRootFiles(DECORATED_FILES)[0]);
+        const host = new Esm2015ReflectionHost(new MockLogger(), false, program.getTypeChecker());
+        const classDecl =
+            getDeclaration(program, DECORATED_FILES[0].name, 'A', ts.isClassDeclaration) !;
+        const classSymbol = host.getClassSymbol(classDecl) !;
+
+        const firstResult = host.getDecoratorsOfSymbol(classSymbol);
+        const secondResult = host.getDecoratorsOfSymbol(classSymbol);
+
+        expect(firstResult).not.toBe(secondResult);
+      });
     });
 
     describe('getDtsDeclarationsOfClass()', () => {