A process for preparing a procatalyst for polymerization of olefins, said process comprising contacting a magnesium-containing support with a halogen-containing titanium compound, a first internal electron donor represented by Formula A, a second internal electron donor represented by Formula B, and an activator; wherein the molar ratio of the first internal electron donor to the second internal electron donor is between 0.01 and 0.7; wherein in Formula A each R 80 group is independently a substituted or unsubstituted aromatic group; R 81, R 82, R 83, R 84, R 85, R 86 and R 87 are each independently selected from a hydrogen or a hydrocarbyl group; N is a nitrogen atom; O is an oxygen atom; and C is a carbon atom; wherein in Formula B R 51 and R 52 are each independently selected from a hydrogen or a hydrocarbyl group; R 53 and R 54 are each independently selected from hydrogen, a halide or a hydrocarbyl group; O is an oxygen atom; and C is a carbon atom; 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 is a hydrocarbyl group, wherein R 4 is butyl; 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; ii) optionally contacting the solid Mg(OR 1) x X 1 2-x obtained in step ii) with at least one activating compound selected from the group formed by activating electron donors and metal alkoxide compounds of formula M1(OR 2) v-w (OR 3) w or M 2 (OR 2) vw (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; R 2 and R 3 are each independently a hydrocarbyl group; w is smaller than v, v is preferably 3 or 4; iii) contacting the first or second intermediate reaction product, obtained respectively in step i) or ii), with the halogen-containing Ti-compound, the first internal electron donor according to Formula A, the second internal electron donor according to Formula B, and the activator. wherein in Formula A each R 80 group is independently a substituted or unsubstituted aromatic group; R 81, R 82, R 83, R 84, R 85, R 86 and R 87 are each independently selected from a hydrogen or a hydrocarbyl group; N is a nitrogen atom; O is an oxygen atom; and C is a carbon atom; wherein in Formula B R 51 and R 52 are each independently selected from a hydrogen or a hydrocarbyl group; R 53 and R 54 are each independently selected from hydrogen, a halide or a hydrocarbyl group; O is an oxygen atom; and C is a carbon atom; 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 is a hydrocarbyl group, wherein R 4 is butyl; 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; ii) optionally contacting the solid Mg(OR 1) x X 1 2-x obtained in step ii) with at least one activating compound selected from the group formed by activating electron donors and metal alkoxide compounds of formula M1(OR 2) v-w (OR 3) w or M 2 (OR 2) vw (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; R 2 and R 3 are each independently a hydrocarbyl group; w is smaller than v, v is preferably 3 or 4; iii) contacting the first or second intermediate reaction product, obtained respectively in step i) or ii), with the halogen-containing Ti-compound, the first internal electron donor according to Formula A, the second internal electron donor according to Formula B, and the activator. 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 is a hydrocarbyl group, wherein R 4 is butyl; 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; ii) optionally contacting the solid Mg(OR 1) x X 1 2-x obtained in step ii) with at least one activating compound selected from the group formed by activating electron donors and metal alkoxide compounds of formula M1(OR 2) v-w (OR 3) w or M 2 (OR 2) vw (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; R 2 and R 3 are each independently a hydrocarbyl group; w is smaller than v, v is preferably 3 or 4; iii) contacting the first or second intermediate reaction product, obtained respectively in step i) or ii), with the halogen-containing Ti-compound, the first internal electron donor according to Formula A, the second internal electron donor according to Formula B, and the activator.