diff --git a/packages/compiler/src/expression_parser/ast.ts b/packages/compiler/src/expression_parser/ast.ts
index 79d822c69e6..c2908e1094c 100644
--- a/packages/compiler/src/expression_parser/ast.ts
+++ b/packages/compiler/src/expression_parser/ast.ts
@@ -320,7 +320,7 @@ export class Binary extends AST {
     return visitor.visitBinary(this, context);
   }
 
-  static isAssignmentOperation(op: string): boolean {
+  static isAssignmentOperation(op: string): op is AssignmentOperation {
     return (
       op === '=' ||
       op === '+=' ||