diff --git a/google/cloud/security/privateca/v1/resources.proto b/google/cloud/security/privateca/v1/resources.proto
index 4da13f433c..e3358bc9f3 100644
--- a/google/cloud/security/privateca/v1/resources.proto
+++ b/google/cloud/security/privateca/v1/resources.proto
@@ -995,15 +995,16 @@ message CertificateIdentityConstraints {
   // https://cloud.google.com/certificate-authority-service/docs/cel-guide
   google.type.Expr cel_expression = 1 [(google.api.field_behavior) = OPTIONAL];
 
-  // Optional. If this is set, the [Subject][google.cloud.security.privateca.v1.Subject] field may be copied from a certificate
+  // Required. If this is true, the [Subject][google.cloud.security.privateca.v1.Subject] field may be copied from a certificate
   // request into the signed certificate. Otherwise, the requested [Subject][google.cloud.security.privateca.v1.Subject]
-  // will be discarded.
-  bool allow_subject_passthrough = 2 [(google.api.field_behavior) = OPTIONAL];
+  // will be discarded. The bool is optional to indicate an unset field, which suggests a forgotten value that needs to be set by the caller.
+  optional bool allow_subject_passthrough = 2 [(google.api.field_behavior) = REQUIRED];
 
-  // Optional. If this is set, the [SubjectAltNames][google.cloud.security.privateca.v1.SubjectAltNames] extension may be copied from a
+  // Required. If this is true, the [SubjectAltNames][google.cloud.security.privateca.v1.SubjectAltNames] extension may be copied from a
   // certificate request into the signed certificate. Otherwise, the requested
   // [SubjectAltNames][google.cloud.security.privateca.v1.SubjectAltNames] will be discarded.
-  bool allow_subject_alt_names_passthrough = 3 [(google.api.field_behavior) = OPTIONAL];
+  // The bool is optional to indicate an unset field, which suggests a forgotten value that needs to be set by the caller.
+  optional bool allow_subject_alt_names_passthrough = 3 [(google.api.field_behavior) = REQUIRED];
 }
 
 // Describes a set of X.509 extensions that may be part of some certificate