Process for preparing an olefin polymerisation catalyst component in the form of solid particles comprising the steps of a) preparing a solution in an organic liquid reaction medium of at least one alkoxy compound (Ax) being the reaction product of at least one compound of a Group 2 metal with at least a monohydric alcohol wherein the solution comprises in addition to the at least one alkoxy compound (Ax) at least one alkoxy compound (Bx) being the reaction product of at least one compound of Group 2 metal and an alcohol comprising in addition to the hydroxyl moiety at least one further oxygen bearing group being different to a hydroxyl moiety, or wherein the alkoxy compound (Ax) is a reaction product of at least one compound of Group 2 metal and a mixture of monohydric alcohol with a further alcohol comprising in addition to the hydroxyl moiety at least one further oxygen bearing group being different to a hydroxyl moiety,, b) adding said solution to at least one compound of a Group 4 metal and c) preparing the solid catalyst component particles, wherein a 1,3-diether of formula or wherein in formula and R 1 and R 2 are the same or different and can be a linear or branched C 1 -C 12 -alkyl, or R 1 with R 5 and/or R 2 with R 6 can form a ring with 4 to 6 C-atoms, R 3 and R 4 of formula are the same or different and can be H or a linear or branched C 1 -C 12 -alkyl or R 3 and R 4 can form together a ring with 5 to 10 C-atoms, which can be part of an aliphatic or aromatic polycyclic ring system with 9 to 20 C atoms, R 5 and R 6 in formula are the same or different and can be H or a linear or branched C 1 -C 12 -alkyl or can form together an aliphatic ring with 5 to 8 C-atoms, and R 51, R 61 and R 7 in formula are the same or different and can be H or a linear or branched C 1 -C 12 -alkyl or two or three of R 51, R 61 and R 7 can form together with C 1 to C 3 an aromatic ring or ring system with 6 to 14 C-atoms, preferably 10 to 14 C-atoms, or mixtures therefrom is added as internal donor at any step prior to step c), wherein no phthalate compound is used in the process. a) preparing a solution in an organic liquid reaction medium of at least one alkoxy compound (Ax) being the reaction product of at least one compound of a Group 2 metal with at least a monohydric alcohol wherein the solution comprises in addition to the at least one alkoxy compound (Ax) at least one alkoxy compound (Bx) being the reaction product of at least one compound of Group 2 metal and an alcohol comprising in addition to the hydroxyl moiety at least one further oxygen bearing group being different to a hydroxyl moiety, or wherein the alkoxy compound (Ax) is a reaction product of at least one compound of Group 2 metal and a mixture of monohydric alcohol with a further alcohol comprising in addition to the hydroxyl moiety at least one further oxygen bearing group being different to a hydroxyl moiety,, b) adding said solution to at least one compound of a Group 4 metal and c) preparing the solid catalyst component particles, R 1 and R 2 are the same or different and can be a linear or branched C 1 -C 12 -alkyl, or R 1 with R 5 and/or R 2 with R 6 can form a ring with 4 to 6 C-atoms, R 3 and R 4 of formula are the same or different and can be H or a linear or branched C 1 -C 12 -alkyl or R 3 and R 4 can form together a ring with 5 to 10 C-atoms, which can be part of an aliphatic or aromatic polycyclic ring system with 9 to 20 C atoms, R 5 and R 6 in formula are the same or different and can be H or a linear or branched C 1 -C 12 -alkyl or can form together an aliphatic ring with 5 to 8 C-atoms, and R 51, R 61 and R 7 in formula are the same or different and can be H or a linear or branched C 1 -C 12 -alkyl or two or three of R 51, R 61 and R 7 can form together with C 1 to C 3 an aromatic ring or ring system with 6 to 14 C-atoms, preferably 10 to 14 C-atoms, or mixtures therefrom is added as internal donor at any step prior to step c), wherein no phthalate compound is used in the process.