diff --git a/CHANGELOG.md b/CHANGELOG.md
index b29ad2f1..585b9725 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,9 @@ All notable changes to this project will be documented in this file.
 - Django 3.1
 - Handle status callbacks from Twilio, show delivery failures in Integrations
 
+## Bug Fixes
+- Handle excessively long email addresses in the signup form.
+
 ## v1.16.0 - 2020-08-04
 
 ### Improvements
diff --git a/hc/accounts/forms.py b/hc/accounts/forms.py
index 48b500b2..3bcc894a 100644
--- a/hc/accounts/forms.py
+++ b/hc/accounts/forms.py
@@ -20,6 +20,9 @@ class AvailableEmailForm(forms.Form):
 
     def clean_identity(self):
         v = self.cleaned_data["identity"]
+        if len(v) > 254:
+            raise forms.ValidationError("Address is too long.")
+
         if User.objects.filter(email=v).exists():
             raise forms.ValidationError(
                 "An account with this email address already exists."
diff --git a/hc/accounts/tests/test_signup.py b/hc/accounts/tests/test_signup.py
index ffba2700..b4bba924 100644
--- a/hc/accounts/tests/test_signup.py
+++ b/hc/accounts/tests/test_signup.py
@@ -81,3 +81,11 @@ class SignupTestCase(TestCase):
         form = {"identity": "alice at example org"}
         r = self.client.post("/accounts/signup/", form)
         self.assertContains(r, "Enter a valid email address")
+
+    def test_it_checks_length(self):
+        aaa = "a" * 300
+        form = {"identity": f"alice+{aaa}@example.org"}
+        r = self.client.post("/accounts/signup/", form)
+        self.assertContains(r, "Address is too long.")
+
+        self.assertFalse(User.objects.exists())