A process is provided for preparing a glyphosate salt solution that comprises potassium and IPA cations in a desired mole ratio, and that has a glyphosate a.e. concentration not less than about 400 g/l. The process includes adding glyphosate acid to a glyphosate potassium salt solution having a glyphosate assay of at least about 40% a.e. by weight, to form a slurry. The process also includes introducing isopropylamine, in an amount sufficient to neutralize the added glyphosate acid, to the slurry with mixing until all glyphosate is dissolved, to form a mixed glyphosate salt solution comprising potassium and IPA cations in the desired mole ratio.