diff --git a/pyscf/tdscf/_lr_eig.py b/pyscf/tdscf/_lr_eig.py
index 328c17319..41206dead 100644
--- a/pyscf/tdscf/_lr_eig.py
+++ b/pyscf/tdscf/_lr_eig.py
@@ -174,7 +174,7 @@ def eigh(aop, x0, precond, tol_residual=1e-5, lindep=1e-12, nroots=1,
             if x0sym is not None:
                 xs_ir = xs_ir[:row0]
 
-        t_size = max(nroots, max_space-len(xs))
+        t_size = min(nroots, len(xs))
         xt = -w[:t_size,None] * xs[:t_size]
         xt += ax[:t_size]
         if x0sym is not None: