diff --git a/api/custom_auth/serializers.py b/api/custom_auth/serializers.py
index fe680fb5af35..55bb43e595ae 100644
--- a/api/custom_auth/serializers.py
+++ b/api/custom_auth/serializers.py
@@ -40,7 +40,7 @@ class Meta(UserCreateSerializer.Meta):
                     UniqueValidator(
                         queryset=FFAdminUser.objects.all(),
                         lookup="iexact",
-                        message="Invalid email address.",
+                        message="Email already exists. Please log in.",
                     )
                 ]
             }
diff --git a/api/tests/unit/custom_auth/test_unit_custom_auth_serializer.py b/api/tests/unit/custom_auth/test_unit_custom_auth_serializer.py
index a00089baaed2..127f5569a3b9 100644
--- a/api/tests/unit/custom_auth/test_unit_custom_auth_serializer.py
+++ b/api/tests/unit/custom_auth/test_unit_custom_auth_serializer.py
@@ -28,7 +28,7 @@ def test_CustomUserCreateSerializer_does_case_insensitive_lookup_with_email(db):
 
     # When
     assert serializer.is_valid() is False
-    assert serializer.errors["email"][0] == "Invalid email address."
+    assert serializer.errors["email"][0] == "Email already exists. Please log in."
 
 
 def test_CustomUserCreateSerializer_calls_is_authentication_method_valid_correctly_if_auth_controller_is_installed(