diff --git a/anymail/backends/base.py b/anymail/backends/base.py
index c947276..af85db2 100644
--- a/anymail/backends/base.py
+++ b/anymail/backends/base.py
@@ -322,11 +322,16 @@ class BasePayload(object):
 
     def set_alternatives(self, alternatives):
         for content, mimetype in alternatives:
-            self.add_alternative(content, mimetype)
+            if mimetype == "text/html":
+                # This assumes that there's at most one html alternative,
+                # and so it should be the html body. (Most ESPs don't
+                # support multiple html alternative parts anyway.)
+                self.set_html_body(content)
+            else:
+                self.add_alternative(content, mimetype)
 
     def add_alternative(self, content, mimetype):
-        raise NotImplementedError("%s.%s must implement add_alternative or set_alternatives" %
-                                  (self.__class__.__module__, self.__class__.__name__))
+        self.unsupported_feature("alternative part with type '%s'" % mimetype)
 
     def set_attachments(self, attachments):
         for attachment in attachments:
diff --git a/anymail/backends/mandrill.py b/anymail/backends/mandrill.py
index 9f540ff..55b8801 100644
--- a/anymail/backends/mandrill.py
+++ b/anymail/backends/mandrill.py
@@ -117,15 +117,10 @@ class MandrillPayload(RequestsPayload):
         self.data["message"]["text"] = body
 
     def set_html_body(self, body):
-        self.data["message"]["html"] = body
-
-    def add_alternative(self, content, mimetype):
-        if mimetype != 'text/html':
-            self.unsupported_feature("alternative part with mimetype '%s'" % mimetype)
-        elif "html" in self.data["message"]:
+        if "html" in self.data["message"]:
+            # second html body could show up through multiple alternatives, or html body + alternative
             self.unsupported_feature("multiple html parts")
-        else:
-            self.set_html_body(content)
+        self.data["message"]["html"] = body
 
     def add_attachment(self, attachment):
         key = "images" if attachment.inline else "attachments"