Error using sym/subsindex (line 1558) Indexing input must be numeric, logical or ':'.

This the simple code, please have a look

syms m

A = [1 2 3; 4 5 6; 7 8 9;];

B = symsum(A(m,m),m,1,3);

Now error is - Error using sym/subsindex (line 1558) Indexing input must be numeric, logical or ':

I know that m is the symbolic variable, not a numerical value, that's why this is the error. Can anyone help me? Thanks in advance.