diff --git a/packager/media/base/widevine_key_source.cc b/packager/media/base/widevine_key_source.cc
index b2eb1d948d..ea63d761b1 100644
--- a/packager/media/base/widevine_key_source.cc
+++ b/packager/media/base/widevine_key_source.cc
@@ -184,7 +184,9 @@ Status WidevineKeySource::FetchKeys(const std::vector<uint8_t>& pssh_data) {
 Status WidevineKeySource::FetchKeys(uint32_t asset_id) {
   base::AutoLock scoped_lock(lock_);
   request_dict_.Clear();
-  request_dict_.SetInteger("asset_id", asset_id);
+  // Javascript/JSON does not support int64_t or unsigned numbers. Use double
+  // instead as 32-bit integer can be lossless represented using double.
+  request_dict_.SetDouble("asset_id", asset_id);
   return FetchKeysInternal(!kEnableKeyRotation, 0, true);
 }
 
@@ -381,12 +383,18 @@ void WidevineKeySource::FillRequest(bool enable_key_rotation,
 
   // Build key rotation fields.
   if (enable_key_rotation) {
-    request_dict_.SetInteger("first_crypto_period_index",
+    // Javascript/JSON does not support int64_t or unsigned numbers. Use double
+    // instead as 32-bit integer can be lossless represented using double.
+    request_dict_.SetDouble("first_crypto_period_index",
                             first_crypto_period_index);
     request_dict_.SetInteger("crypto_period_count", crypto_period_count_);
   }
 
-  base::JSONWriter::Write(request_dict_, request);
+  base::JSONWriter::WriteWithOptions(
+      request_dict_,
+      // Write doubles that have no fractional part as a normal integer, i.e.
+      // without using exponential notation or appending a '.0'.
+      base::JSONWriter::OPTIONS_OMIT_DOUBLE_TYPE_PRESERVATION, request);
 }
 
 Status WidevineKeySource::GenerateKeyMessage(const std::string& request,
diff --git a/packager/media/base/widevine_key_source_unittest.cc b/packager/media/base/widevine_key_source_unittest.cc
index beb10ab8df..e214134805 100644
--- a/packager/media/base/widevine_key_source_unittest.cc
+++ b/packager/media/base/widevine_key_source_unittest.cc
@@ -43,6 +43,12 @@ const char kLicenseStatusUnknownError[] = "UNKNOWN_ERROR";
 const char kExpectedRequestMessageFormat[] =
     "{\"content_id\":\"%s\",\"drm_types\":[\"WIDEVINE\"],\"policy\":\"%s\","
     "\"tracks\":[{\"type\":\"SD\"},{\"type\":\"HD\"},{\"type\":\"AUDIO\"}]}";
+const char kExpectedRequestMessageWithAssetIdFormat[] =
+    "{\"asset_id\":%u,\"drm_types\":[\"WIDEVINE\"],"
+    "\"tracks\":[{\"type\":\"SD\"},{\"type\":\"HD\"},{\"type\":\"AUDIO\"}]}";
+const char kExpectedRequestMessageWithPsshFormat[] =
+    "{\"drm_types\":[\"WIDEVINE\"],\"pssh_data\":\"%s\","
+    "\"tracks\":[{\"type\":\"SD\"},{\"type\":\"HD\"},{\"type\":\"AUDIO\"}]}";
 const char kExpectedSignedMessageFormat[] =
     "{\"request\":\"%s\",\"signature\":\"%s\",\"signer\":\"%s\"}";
 const char kTrackFormat[] =
@@ -52,7 +58,9 @@ const char kClassicTrackFormat[] = "{\"type\":\"%s\",\"key\":\"%s\"}";
 const char kLicenseResponseFormat[] = "{\"status\":\"%s\",\"tracks\":[%s]}";
 const char kHttpResponseFormat[] = "{\"response\":\"%s\"}";
 const char kRequestPsshData[] = "PSSH data";
-const uint32_t kClassicAssetId = 1234;
+// 32-bit with leading bit set, to verify that big uint32_t can be handled
+// correctly.
+const uint32_t kClassicAssetId = 0x80038cd9;
 
 std::string Base64Encode(const std::string& input) {
   std::string output;
@@ -212,7 +220,8 @@ TEST_F(WidevineKeySourceTest, GenerateSignatureFailure) {
 TEST_F(WidevineKeySourceTest, HttpFetchFailure) {
   std::string expected_message = base::StringPrintf(
       kExpectedRequestMessageFormat, Base64Encode(kContentId).c_str(), kPolicy);
-  EXPECT_CALL(*mock_request_signer_, GenerateSignature(expected_message, _))
+  EXPECT_CALL(*mock_request_signer_,
+              GenerateSignature(StrEq(expected_message), _))
       .WillOnce(DoAll(SetArgPointee<1>(kMockSignature), Return(true)));
 
   std::string expected_post_data =
@@ -258,29 +267,43 @@ TEST_F(WidevineKeySourceTest, LicenseStatusCencNotOK) {
 }
 
 TEST_F(WidevineKeySourceTest, LicenseStatusCencWithPsshDataOK) {
+  std::string expected_message =
+      base::StringPrintf(kExpectedRequestMessageWithPsshFormat,
+                         Base64Encode(kRequestPsshData).c_str());
+  EXPECT_CALL(*mock_request_signer_,
+              GenerateSignature(StrEq(expected_message), _))
+      .WillOnce(DoAll(SetArgPointee<1>(kMockSignature), Return(true)));
+
   std::string mock_response = base::StringPrintf(
       kHttpResponseFormat, Base64Encode(GenerateMockLicenseResponse()).c_str());
-
   EXPECT_CALL(*mock_key_fetcher_, FetchKeys(_, _, _))
       .WillOnce(DoAll(SetArgPointee<2>(mock_response), Return(Status::OK)));
 
   CreateWidevineKeySource();
+  widevine_key_source_->set_signer(mock_request_signer_.Pass());
   std::vector<uint8_t> pssh_data(
       reinterpret_cast<const uint8_t*>(kRequestPsshData),
-      reinterpret_cast<const uint8_t*>(kRequestPsshData) + strlen(kContentId));
+      reinterpret_cast<const uint8_t*>(kRequestPsshData) +
+          strlen(kRequestPsshData));
   ASSERT_OK(widevine_key_source_->FetchKeys(pssh_data));
   VerifyKeys(false);
 }
 
 TEST_F(WidevineKeySourceTest, LicenseStatusClassicOK) {
+  std::string expected_message = base::StringPrintf(
+      kExpectedRequestMessageWithAssetIdFormat, kClassicAssetId);
+  EXPECT_CALL(*mock_request_signer_,
+              GenerateSignature(StrEq(expected_message), _))
+      .WillOnce(DoAll(SetArgPointee<1>(kMockSignature), Return(true)));
+
   std::string mock_response = base::StringPrintf(
       kHttpResponseFormat, Base64Encode(
           GenerateMockClassicLicenseResponse()).c_str());
-
   EXPECT_CALL(*mock_key_fetcher_, FetchKeys(_, _, _))
       .WillOnce(DoAll(SetArgPointee<2>(mock_response), Return(Status::OK)));
 
   CreateWidevineKeySource();
+  widevine_key_source_->set_signer(mock_request_signer_.Pass());
   ASSERT_OK(widevine_key_source_->FetchKeys(kClassicAssetId));
   VerifyKeys(true);
 }