Div by 0 error - SQL server

Hi,

I have this SQL below.. I get div by 0 error. Can anyone help please?

case when sum(CASE  WHEN  tab1.col = 'R010' And tab2.col = '2015'

  THEN tab3.MthValue ELSE 0 END)=0 then 0 ELSE  Sum(CASE  WHEN  tab1.col = 'R010' And tab2.col = '2015'

  THEN tab3.MthValue ELSE 0 END)-Sum(CASE  WHEN  tab1.col = 'R010' And tab2.col = '2015'

  THEN tab3.MthValue ELSE 100 END)/Sum(CASE  WHEN  tab1.col = 'R010' And tab2.col = '2015'

  THEN tab3.MthValue ELSE 0 END) end  as '%'

Thank You

Veena M