diff --git a/tools/@aws-cdk/spec2cdk/lib/cdk/resource-decider.ts b/tools/@aws-cdk/spec2cdk/lib/cdk/resource-decider.ts
index b4548d732902b..913f8459856b0 100644
--- a/tools/@aws-cdk/spec2cdk/lib/cdk/resource-decider.ts
+++ b/tools/@aws-cdk/spec2cdk/lib/cdk/resource-decider.ts
@@ -77,6 +77,7 @@ export class ResourceDecider {
         remarks: (propSpec.docs?.remarks ?? '').concat('@cloudformationAttribute Ref'),
       },
       immutable: true,
+      optional: false,
     };
   }
 
diff --git a/tools/@aws-cdk/spec2cdk/test/__snapshots__/resources.test.ts.snap b/tools/@aws-cdk/spec2cdk/test/__snapshots__/resources.test.ts.snap
index 2129619e82fd9..656dc73d1e741 100644
--- a/tools/@aws-cdk/spec2cdk/test/__snapshots__/resources.test.ts.snap
+++ b/tools/@aws-cdk/spec2cdk/test/__snapshots__/resources.test.ts.snap
@@ -18,7 +18,7 @@ export interface ICfnResource extends constructs.IConstruct {
    *
    * @cloudformationAttribute Ref
    */
-  readonly attrId?: string;
+  readonly attrId: string;
 }
 
 /**
@@ -62,7 +62,7 @@ export class CfnResource extends cdk.CfnResource implements cdk.IInspectable, IC
    *
    * @cloudformationAttribute Ref
    */
-  public readonly attrId?: string;
+  public readonly attrId: string;
 
   /**
    * The identifier of the resource.
@@ -1107,14 +1107,14 @@ import * as cfn_parse from "aws-cdk-lib/core/lib/helpers-internal";
  *
  * @stability external
  */
-export interface ICfnResource {
+export interface ICfnResource extends constructs.IConstruct {
   /**
    * The identifier of the resource.
    * This property gets determined after the resource is created.
    *
    * @cloudformationAttribute Ref
    */
-  readonly attrId?: string;
+  readonly attrId: string;
 
   /**
    * Another identifier of the resource.
@@ -1122,7 +1122,7 @@ export interface ICfnResource {
    *
    * @cloudformationAttribute Ref
    */
-  readonly attrAnotherId?: string;
+  readonly attrAnotherId: string;
 }
 
 /**
@@ -1166,7 +1166,7 @@ export class CfnResource extends cdk.CfnResource implements cdk.IInspectable, IC
    *
    * @cloudformationAttribute Ref
    */
-  public readonly attrAnotherId?: string;
+  public readonly attrAnotherId: string;
 
   /**
    * The identifier of the resource.
@@ -1174,7 +1174,7 @@ export class CfnResource extends cdk.CfnResource implements cdk.IInspectable, IC
    *
    * @cloudformationAttribute Ref
    */
-  public readonly attrId?: string;
+  public readonly attrId: string;
 
   /**
    * Another identifier of the resource.
@@ -1305,14 +1305,14 @@ import * as cfn_parse from "aws-cdk-lib/core/lib/helpers-internal";
  *
  * @stability external
  */
-export interface ICfnResource {
+export interface ICfnResource extends constructs.IConstruct {
   /**
    * The identifier of the resource.
    * This property gets determined after the resource is created.
    *
    * @cloudformationAttribute Ref
    */
-  readonly attrId?: string;
+  readonly attrId: string;
 }
 
 /**
@@ -1356,7 +1356,7 @@ export class CfnResource extends cdk.CfnResource implements cdk.IInspectable, IC
    *
    * @cloudformationAttribute Ref
    */
-  public readonly attrId?: string;
+  public readonly attrId: string;
 
   /**
    * The identifier of the resource.