diff --git a/coldfront/core/project/exceptions.py b/coldfront/core/project/exceptions.py
new file mode 100644
index 0000000000..e5247f8b94
--- /dev/null
+++ b/coldfront/core/project/exceptions.py
@@ -0,0 +1,14 @@
+"""Exceptions raised when integrations (e.g. LDAP) reject a project-user change.
+
+Plugins that hook into project signals (see coldfront.core.project.signals) should
+raise these -- or subclasses of these -- rather than plugin-specific exception types,
+so core code can handle the failure without importing from any plugin.
+"""
+
+
+class ProjectUserAdditionError(Exception):
+    """Raised when a user cannot be added to a project by a signal receiver."""
+
+
+class ProjectUserDeactivatedError(ProjectUserAdditionError):
+    """Raised when a user cannot be added to a project because their account is deactivated."""
diff --git a/coldfront/core/project/views.py b/coldfront/core/project/views.py
index f7f40b13cb..1bf43319bc 100644
--- a/coldfront/core/project/views.py
+++ b/coldfront/core/project/views.py
@@ -66,6 +66,7 @@
 )
 from coldfront.core.project.manager_role_notifications import notify_manager_role_transition
 from coldfront.core.project.utils import generate_usage_history_graph
+from coldfront.core.project.exceptions import ProjectUserDeactivatedError
 from coldfront.core.publication.models import Publication
 from coldfront.core.research_output.models import ResearchOutput
 from coldfront.core.resource.models import ResourceAttribute
@@ -825,6 +826,12 @@ def post(self, request, *args, **kwargs):
                             sender=self.__class__,
                             user_name=user_obj.username, group_name=project_obj.title
                         )
+                    except ProjectUserDeactivatedError:
+                        errors.append(
+                            f"Could not add user {user_obj} to project {project_obj.title}: "
+                            "this user's account is deactivated."
+                        )
+                        continue
                     except Exception as e:
                         logger.exception(
                             'AD user addition to group failed.',
diff --git a/coldfront/plugins/ldap/signals.py b/coldfront/plugins/ldap/signals.py
index 786a181e03..e4664d1fb6 100644
--- a/coldfront/plugins/ldap/signals.py
+++ b/coldfront/plugins/ldap/signals.py
@@ -19,7 +19,7 @@
     ProjectUserStatusChoice,
     ProjectUser,
 )
-from coldfront.plugins.ldap.utils import LDAPConn
+from coldfront.plugins.ldap.utils import LDAPConn, LDAPUserDeactivatedError
 
 if 'sftocf' in import_from_settings('INSTALLED_APPS', []):
     from sftocf.signals import (
@@ -138,7 +138,19 @@ def filter_project_users_to_remove(sender, **kwargs):
 @receiver(project_make_projectuser)
 def add_user_to_group(sender, **kwargs):
     ldap_conn = LDAPConn()
-    ldap_conn.add_user_to_group(kwargs['user_name'], kwargs['group_name'])
+    try:
+        ldap_conn.add_user_to_group(kwargs['user_name'], kwargs['group_name'])
+    except LDAPUserDeactivatedError:
+        logger.warning(
+            'Cannot add deactivated user to AD group.',
+            extra={
+                'category': 'ldap:GroupMembership',
+                'status': 'error',
+                'user': kwargs['user_name'],
+                'group': kwargs['group_name'],
+            }
+        )
+        raise
 
 @receiver(project_preremove_projectuser)
 def remove_member_from_group(sender, **kwargs):
diff --git a/coldfront/plugins/ldap/utils.py b/coldfront/plugins/ldap/utils.py
index 04f0b62666..97a02dac12 100644
--- a/coldfront/plugins/ldap/utils.py
+++ b/coldfront/plugins/ldap/utils.py
@@ -32,6 +32,7 @@
     ProjectUserStatusChoice,
     ProjectUser,
 )
+from coldfront.core.project.exceptions import ProjectUserDeactivatedError
 
 
 logger = logging.getLogger(__name__)
@@ -48,6 +49,9 @@ class LDAPException(Exception):
 class LDAPUserAdditionError(LDAPException):
     """An exception raised when a user cannot be added to an LDAP Group"""
 
+class LDAPUserDeactivatedError(LDAPUserAdditionError, ProjectUserDeactivatedError):
+    """An exception raised when a user cannot be added to an LDAP Group because their account is deactivated"""
+
 class LDAPUserRemovalError(LDAPException):
     """An exception raised when a user cannot be removed from an LDAP Group"""
 
@@ -211,6 +215,10 @@ def return_project_ldap_groups(self, attributes=('sAMAccountName',), groups=('*_
 
     def add_user_to_group(self, user_name, group_name):
         user = self.return_user_by_name(user_name)
+        if not user_valid(user):
+            raise LDAPUserDeactivatedError(
+                f"Cannot add user {user_name} to group {group_name}: user is deactivated."
+            )
         group = self.return_group_by_name(group_name)
         self.add_member_to_group(user, group)