diff --git a/identity/aidl/default/WritableIdentityCredential.cpp b/identity/aidl/default/WritableIdentityCredential.cpp
index b392444..8bc4b49 100644
--- a/identity/aidl/default/WritableIdentityCredential.cpp
+++ b/identity/aidl/default/WritableIdentityCredential.cpp
@@ -22,6 +22,7 @@
 #include <android/hardware/identity/support/IdentityCredentialSupport.h>
 
 #include <android-base/logging.h>
+#include <android-base/stringprintf.h>
 
 #include <cppbor/cppbor.h>
 #include <cppbor/cppbor_parse.h>
@@ -34,6 +35,7 @@
 
 namespace aidl::android::hardware::identity {
 
+using ::android::base::StringPrintf;
 using ::std::optional;
 using namespace ::android::hardware::identity;
 
@@ -105,6 +107,12 @@
     return ndk::ScopedAStatus::ok();
 }
 
+ndk::ScopedAStatus WritableIdentityCredential::setExpectedProofOfProvisioningSize(
+        int32_t expectedProofOfProvisioningSize) {
+    expectedProofOfProvisioningSize_ = expectedProofOfProvisioningSize;
+    return ndk::ScopedAStatus::ok();
+}
+
 ndk::ScopedAStatus WritableIdentityCredential::startPersonalization(
         int32_t accessControlProfileCount, const vector<int32_t>& entryCounts) {
     if (startPersonalizationCalled_) {
@@ -382,6 +390,16 @@
             .add(testCredential_);
     vector<uint8_t> encodedCbor = popArray.encode();
 
+    if (encodedCbor.size() != expectedProofOfProvisioningSize_) {
+        LOG(ERROR) << "CBOR for proofOfProvisioning is " << encodedCbor.size() << " bytes, "
+                   << "was expecting " << expectedProofOfProvisioningSize_;
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_INVALID_DATA,
+                StringPrintf("Unexpected CBOR size %zd for proofOfProvisioning, was expecting %zd",
+                             encodedCbor.size(), expectedProofOfProvisioningSize_)
+                        .c_str()));
+    }
+
     optional<vector<uint8_t>> signature = support::coseSignEcDsa(credentialPrivKey_,
                                                                  encodedCbor,  // payload
                                                                  {},           // additionalData