diff --git a/libwvdrmengine/oemcrypto/mock/src/oemcrypto_session.cpp b/libwvdrmengine/oemcrypto/mock/src/oemcrypto_session.cpp
index e409c0f0..c392e19f 100644
--- a/libwvdrmengine/oemcrypto/mock/src/oemcrypto_session.cpp
+++ b/libwvdrmengine/oemcrypto/mock/src/oemcrypto_session.cpp
@@ -192,9 +192,14 @@ bool SessionContext::GenerateSignature(const uint8_t* message,
     return false;
   }
 
-  if (mac_key_client_.empty() ||
-      mac_key_client_.size() != wvcdm::MAC_KEY_SIZE) {
-    LOGE("[GenerateSignature(): No MAC Key]");
+  const uint8_t *mac_key = NULL;
+  if (mac_key_client_.size() == wvcdm::MAC_KEY_SIZE) {
+    // If we have a mac key, use it.
+    mac_key = &mac_key_client_[0];
+  } else if (usage_entry_status_ == kUsageEntryLoaded) {
+    // If not, but we have a usage entry, use its key.
+    mac_key = usage_entry_->mac_key_client();
+  } else {
     return false;
   }
 
@@ -204,7 +209,7 @@ bool SessionContext::GenerateSignature(const uint8_t* message,
   }
 
   unsigned int md_len = *signature_length;
-  if (HMAC(EVP_sha256(), &mac_key_client_[0], mac_key_client_.size(), message,
+  if (HMAC(EVP_sha256(), mac_key, wvcdm::MAC_KEY_SIZE, message,
            message_length, signature, &md_len)) {
     *signature_length = md_len;
     return true;
diff --git a/libwvdrmengine/oemcrypto/mock/src/oemcrypto_usage_table_mock.h b/libwvdrmengine/oemcrypto/mock/src/oemcrypto_usage_table_mock.h
index 0afc00c9..4ec70bec 100644
--- a/libwvdrmengine/oemcrypto/mock/src/oemcrypto_usage_table_mock.h
+++ b/libwvdrmengine/oemcrypto/mock/src/oemcrypto_usage_table_mock.h
@@ -69,6 +69,8 @@ class UsageTableEntry {
   void set_index(int32_t index) { data_.index = index; }
   uint32_t index() { return data_.index; }
   static size_t SignedEntrySize();
+  const uint8_t* mac_key_server() { return data_.mac_key_server; }
+  const uint8_t* mac_key_client() { return data_.mac_key_client; }
 
  private:
   UsageTable* usage_table_;  // Owner of this object.
diff --git a/libwvdrmengine/oemcrypto/test/oec_session_util.cpp b/libwvdrmengine/oemcrypto/test/oec_session_util.cpp
index 581c1564..927d6a80 100644
--- a/libwvdrmengine/oemcrypto/test/oec_session_util.cpp
+++ b/libwvdrmengine/oemcrypto/test/oec_session_util.cpp
@@ -927,6 +927,9 @@ void Session::GenerateReport(const std::string& pst,
   EXPECT_GE(kHardwareSecureClock, pst_report().clock_security_level());
   EXPECT_EQ(pst.length(), pst_report().pst_length());
   EXPECT_EQ(0, memcmp(pst.c_str(), pst_report().pst(), pst.length()));
+  // Also, we the session to be able to sign the release message with the
+  // correct mac keys from the usage table entry.
+  ASSERT_NO_FATAL_FAILURE(VerifyClientSignature());
 }
 
 void Session::VerifyPST(const Test_PST_Report& expected) {
diff --git a/libwvdrmengine/oemcrypto/test/oec_session_util.h b/libwvdrmengine/oemcrypto/test/oec_session_util.h
index 578e5e85..e7c992e7 100644
--- a/libwvdrmengine/oemcrypto/test/oec_session_util.h
+++ b/libwvdrmengine/oemcrypto/test/oec_session_util.h
@@ -293,7 +293,8 @@ class Session {
   wvcdm::Unpacked_PST_Report pst_report() {
     return wvcdm::Unpacked_PST_Report(&pst_report_buffer_[0]);
   }
-  // Verify the PST report.
+  // Verify the values in the PST report.  The signature should have been
+  // verified in GenerateReport, above.
   void VerifyPST(const Test_PST_Report& report);
   // Generate and Verify the Usage Report. If any time is greater than 10
   // minutes, it is assumed to be an absolute time, and time_since will be