A process for preparing a procatalyst for polymerization of olefins, said process comprising contacting a magnesium-containing support with a halogen-containing titanium compound, an internal electron donor being a substituted 1,2-phenylene aromatic diester compound according to Formula A, and optionally an activator being a monoamide and/or a monoester wherein in Formula A R 11, R 12, R 13, R 14, R 15, R 15', R 16, R 16', R 17, R 17', R 18, R 18', R 19, and R 19' are the same or different; and wherein each of these R-groups is independently selected from the group consisting of hydrogen, a substituted hydrocarbyl group having 1 to 20 carbon atoms, an unsubstituted hydrocarbyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a heteroatom, and combinations thereof; and on the proviso that not all of R-groups may be hydrogen; wherein said process comprises the steps of: i) contacting a compound R 4 z MgX 4 2-z with an alkoxy- or aryloxy-containing silane compound to give a first intermediate reaction product, being a solid Mg(OR 1) x X 1 2-x, wherein R 1 and R 4 are independently selected from linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, or alkylaryl groups, and one or more combinations thereof; wherein said hydrocarbyl group may be substituted or unsubstituted, may contain one or more heteroatoms and preferably has from 1 to 20 carbon atoms; wherein X 4 and X 1 are each independently a halide; z is in a range of larger than 0 and smaller than 2, being 0 < z < 2; x is in a range of larger than 0 and smaller than 2, being 0 < x < 2 to obtain a first intermediate product; ii) optionally contacting the solid Mg(OR 1) x X 1 2-x obtained in step i) with at least one activating compound selected from the group formed by activating electron donors and metal alkoxide compounds of formula M 1 (OR 2) v-w (OR 3) w or M 2 (OR 2) v-w (R 3) w, to obtain a second intermediate product; wherein: M 1 is a metal selected from the group consisting of Ti, Zr, Hf, Al or Si; v is the valency of M 1; M 2 is a metal being Si; v is the valency of M 2; v is preferably 3 or 4, and w is smaller than v; R 2 and R 3 are each a linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof; wherein said hydrocarbyl group may be substituted or unsubstituted, may contain one or more heteroatoms, and preferably has from 1 to 20 carbon atoms; iii-1) contacting the first intermediate reaction product, obtained in step i) or the second intermediate reaction product, obtained in step ii) with the halogen-containing titanium compound and optionally the activator, and reaction of the mixture and subsequent washing of the mixture to obtain a third intermediate product; iv-a) contacting the third intermediate product obtained in step iii-1) with the halogen-containing titanium compound and the internal electron donor according to Formula A and reaction of the mixture to obtain a fourth intermediate product; v) contacting the fourth intermediate product obtained in step iv) with the halogen-containing Ti-compound to obtain the procatalyst. i) contacting a compound R 4 z MgX 4 2-z with an alkoxy- or aryloxy-containing silane compound to give a first intermediate reaction product, being a solid Mg(OR 1) x X 1 2-x, wherein R 1 and R 4 are independently selected from linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, or alkylaryl groups, and one or more combinations thereof; wherein said hydrocarbyl group may be substituted or unsubstituted, may contain one or more heteroatoms and preferably has from 1 to 20 carbon atoms; wherein X 4 and X 1 are each independently a halide; z is in a range of larger than 0 and smaller than 2, being 0 < z < 2; x is in a range of larger than 0 and smaller than 2, being 0 < x < 2 to obtain a first intermediate product; ii) optionally contacting the solid Mg(OR 1) x X 1 2-x obtained in step i) with at least one activating compound selected from the group formed by activating electron donors and metal alkoxide compounds of formula M 1 (OR 2) v-w (OR 3) w or M 2 (OR 2) v-w (R 3) w, to obtain a second intermediate product; wherein: M 1 is a metal selected from the group consisting of Ti, Zr, Hf, Al or Si; v is the valency of M 1; M 2 is a metal being Si; v is the valency of M 2; v is preferably 3 or 4, and w is smaller than v; R 2 and R 3 are each a linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof; wherein said hydrocarbyl group may be substituted or unsubstituted, may contain one or more heteroatoms, and preferably has from 1 to 20 carbon atoms; iii-1) contacting the first intermediate reaction product, obtained in step i) or the second intermediate reaction product, obtained in step ii) with the halogen-containing titanium compound and optionally the activator, and reaction of the mixture and subsequent washing of the mixture to obtain a third intermediate product; iv-a) contacting the third intermediate product obtained in step iii-1) with the halogen-containing titanium compound and the internal electron donor according to Formula A and reaction of the mixture to obtain a fourth intermediate product; v) contacting the fourth intermediate product obtained in step iv) with the halogen-containing Ti-compound to obtain the procatalyst.