diff --git a/anymail/backends/sendgrid.py b/anymail/backends/sendgrid.py
index e3015d2..9bf2232 100644
--- a/anymail/backends/sendgrid.py
+++ b/anymail/backends/sendgrid.py
@@ -69,7 +69,7 @@ class SendGridPayload(RequestsPayload):
         self.generate_message_id = backend.generate_message_id
         self.message_id = None  # Message-ID -- assigned in serialize_data unless provided in headers
         self.smtpapi = {}  # SendGrid x-smtpapi field
-        self.to_list = []  # late-bound 'to' field
+        self.to_list = []  # needed for build_merge_data
         self.merge_field_format = backend.merge_field_format
         self.merge_data = None  # late-bound per-recipient data
         self.merge_global_data = None
@@ -95,14 +95,10 @@ class SendGridPayload(RequestsPayload):
             self.ensure_message_id()
 
         self.build_merge_data()
-        if self.merge_data is None:
-            # Standard 'to' and 'toname' headers
-            self.set_recipients('to', self.to_list)
-        else:
-            # Merge-friendly smtpapi 'to' field
-            self.set_recipients('to', self.to_list)
+        if self.merge_data is not None:
+            # Must *also* set smtpapi 'to' field so SG does batch send
+            # (else all recipients would see each other's emails)
             self.smtpapi['to'] = [email.address for email in self.to_list]
-            self.all_recipients += self.to_list
 
         # Serialize x-smtpapi to json:
         if len(self.smtpapi) > 0:
@@ -200,9 +196,8 @@ class SendGridPayload(RequestsPayload):
             self.data["fromname"] = email.name
 
     def set_to(self, emails):
-        # late-bind in self.serialize_data, because whether it goes in smtpapi
-        # depends on whether there is merge_data
-        self.to_list = emails
+        self.to_list = emails  # track for later use by build_merge_data
+        self.set_recipients('to', emails)
 
     def set_recipients(self, recipient_type, emails):
         assert recipient_type in ["to", "cc", "bcc"]
diff --git a/tests/test_sendgrid_backend.py b/tests/test_sendgrid_backend.py
index 3c2f905..23e1ef2 100644
--- a/tests/test_sendgrid_backend.py
+++ b/tests/test_sendgrid_backend.py
@@ -431,6 +431,7 @@ class SendGridBackendAnymailFeatureTests(SendGridBackendMockAPITestCase):
 
         data = self.get_api_call_data()
         smtpapi = self.get_smtpapi()
+        # For batch send, must set both to+toname *and* smtpapi['to']:
         self.assertEqual(data['toname'], [' ', 'Bob'])
         self.assertEqual(data['to'], ['alice@example.com', 'bob@example.com'])
         self.assertEqual(smtpapi['to'], ['alice@example.com', 'Bob <bob@example.com>'])
diff --git a/tests/test_sendgrid_integration.py b/tests/test_sendgrid_integration.py
index 3bc46a8..15f3bf9 100644
--- a/tests/test_sendgrid_integration.py
+++ b/tests/test_sendgrid_integration.py
@@ -89,6 +89,25 @@ class SendGridBackendIntegrationTests(SimpleTestCase, AnymailTestMixin):
         message.send()
         self.assertEqual(message.anymail_status.status, {'queued'})  # SendGrid always queues
 
+    def test_merge_data(self):
+        message = AnymailMessage(
+            subject="Anymail merge_data test: %value%",
+            body="This body includes merge data: %value%",
+            from_email="Test From <from@example.com>",
+            to=["to1@sink.sendgrid.net", "Recipient 2 <to2@sink.sendgrid.net>"],
+            merge_data={
+                'to1@sink.sendgrid.net': {'value': 'one'},
+                'to2@sink.sendgrid.net': {'value': 'two'},
+            },
+            esp_extra={
+                'merge_field_format': '%{}%',
+            },
+        )
+        message.send()
+        recipient_status = message.anymail_status.recipients
+        self.assertEqual(recipient_status['to1@sink.sendgrid.net'].status, 'queued')
+        self.assertEqual(recipient_status['to2@sink.sendgrid.net'].status, 'queued')
+
     @override_settings(ANYMAIL_SENDGRID_API_KEY="Hey, that's not an API key!")
     def test_invalid_api_key(self):
         with self.assertRaises(AnymailAPIError) as cm: