diff --git a/.eslintrc.json b/.eslintrc.json
index d238f72b1b..7752baad06 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -18,6 +18,7 @@
         "Dropbox": false,
         "SockJS": false,
         "marked": false,
+        "md5": false,
         "moment": false,
         "i18n": false,
         "DynamicText": false,
diff --git a/frontend_tests/node_tests/people.js b/frontend_tests/node_tests/people.js
index 8802f34fd8..d754b7928f 100644
--- a/frontend_tests/node_tests/people.js
+++ b/frontend_tests/node_tests/people.js
@@ -1,12 +1,13 @@
-add_dependencies({
-    util: 'js/util.js',
-});
+zrequire('util');
+zrequire('people');
 
-var people = require("js/people.js");
 set_global('blueslip', {
     error: function () { return undefined; },
 });
 set_global('page_params', {});
+set_global('md5', function (s) {
+    return 'md5-' + s;
+});
 
 var _ = global._;
 
@@ -393,6 +394,23 @@ initialize();
     assert.equal(people.small_avatar_url(message),
         'legacy.png&s=50');
 
+    message = {
+        avatar_url: undefined,
+        sender_id: maria.user_id,
+    };
+    assert.equal(people.small_avatar_url(message),
+        'https://secure.gravatar.com/avatar/md5-athens@example.com?d=identicon&s=50'
+    );
+
+    message = {
+        avatar_url: undefined,
+        sender_email: 'foo@example.com',
+        sender_id: 9999999,
+    };
+    assert.equal(people.small_avatar_url(message),
+        'https://secure.gravatar.com/avatar/md5-foo@example.com?d=identicon&s=50'
+    );
+
     message = {
         type: 'private',
         display_recipient: [
diff --git a/package.json b/package.json
index 7f9a5c4ac9..cbb2c2e3a1 100644
--- a/package.json
+++ b/package.json
@@ -7,6 +7,7 @@
   "dependencies": {
     "@types/node": "8.0.34",
     "@types/webpack": "3.0.13",
+    "blueimp-md5": "2.10.0",
     "clipboard": "1.5.16",
     "emoji-datasource": "3.0.0",
     "emoji-datasource-apple": "3.0.0",
diff --git a/static/js/people.js b/static/js/people.js
index 2dfbd65ae6..9db02b7606 100644
--- a/static/js/people.js
+++ b/static/js/people.js
@@ -508,16 +508,31 @@ exports.small_avatar_url = function (message) {
         person = exports.get_person_from_user_id(message.sender_id);
     }
 
+    var email;
+
     // The first time we encounter a sender in a message, we may
     // not have person.avatar_url set, but if we do, then use that.
-    if (person && person.avatar_url) {
+    if (person) {
         url = person.avatar_url;
-    } else if (message.avatar_url) {
-        // Here we fall back to using the avatar_url from the message
-        // itself.
+        email = person.email;
+    }
+
+    // Try to get info from the message if we didn't have a `person` object
+    // or if the avatar was missing. We do this verbosely to avoid false
+    // positives on line coverage (we don't do branch checking).
+    if (!url) {
         url = message.avatar_url;
     }
 
+    if (!email) {
+        email = message.sender_email;
+    }
+
+    if (!url) {
+        var hash = md5(email);
+        url = 'https://secure.gravatar.com/avatar/' + hash + '?d=identicon';
+    }
+
     if (url) {
         url = exports.format_small_avatar_url(url);
     }
diff --git a/yarn.lock b/yarn.lock
index d0194f1e7a..897cfef17f 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -412,6 +412,10 @@ block-stream@*:
   dependencies:
     inherits "~2.0.0"
 
+blueimp-md5@2.10.0:
+  version "2.10.0"
+  resolved "https://registry.yarnpkg.com/blueimp-md5/-/blueimp-md5-2.10.0.tgz#02f0843921f90dca14f5b8920a38593201d6964d"
+
 bn.js@^4.0.0, bn.js@^4.1.0, bn.js@^4.1.1, bn.js@^4.11.6, bn.js@^4.4.0:
   version "4.11.6"
   resolved "https://registry.yarnpkg.com/bn.js/-/bn.js-4.11.6.tgz#53344adb14617a13f6e8dd2ce28905d1c0ba3215"
diff --git a/zproject/settings.py b/zproject/settings.py
index 17f4796ca6..11ab7b886d 100644
--- a/zproject/settings.py
+++ b/zproject/settings.py
@@ -894,6 +894,7 @@ JS_SPECS = {
             'third/bootstrap-notify/js/bootstrap-notify.js',
             'third/html5-formdata/formdata.js',
             'node_modules/jquery-validation/dist/jquery.validate.js',
+            'node_modules/blueimp-md5/js/md5.js',
             'node_modules/clipboard/dist/clipboard.js',
             'third/jquery-form/jquery.form.js',
             'third/jquery-filedrop/jquery.filedrop.js',