diff --git a/changelog/unreleased/fix-nil-exception-groups.md b/changelog/unreleased/fix-nil-exception-groups.md
new file mode 100644
index 0000000000..5c773e529f
--- /dev/null
+++ b/changelog/unreleased/fix-nil-exception-groups.md
@@ -0,0 +1,3 @@
+Bugfix: Fix nil pointer exception when resolving members of a group (rest driver)
+
+https://github.com/cs3org/reva/pull/2265
\ No newline at end of file
diff --git a/pkg/cbox/group/rest/rest.go b/pkg/cbox/group/rest/rest.go
index 2e93809d60..439ec9c6c9 100644
--- a/pkg/cbox/group/rest/rest.go
+++ b/pkg/cbox/group/rest/rest.go
@@ -346,7 +346,9 @@ func (m *manager) GetMembers(ctx context.Context, gid *grouppb.GroupId) ([]*user
 		if !ok {
 			return nil, errors.New("rest: error in type assertion")
 		}
-		users = append(users, &userpb.UserId{OpaqueId: userInfo["upn"].(string), Idp: m.conf.IDProvider})
+		if id, ok := userInfo["upn"].(string); ok {
+			users = append(users, &userpb.UserId{OpaqueId: id, Idp: m.conf.IDProvider})
+		}
 	}
 
 	if err = m.cacheGroupMembers(gid, users); err != nil {