A coating composition for application on a porous substrate for use with a roller printing application. The coating composition comprises an ethoxylated polyethyleneimine polymer, a pH modifier, a thickening additive, an ammonium sulfate, a surfactant, and water. Optional additives can comprise a biocide, a lower aliphatic alcohol and a UV fluorescent dye. When the coating composition is applied to the porous substrate, waterfast prints are produced which are resistant to smudging or bleeding when subjected to moisture. The coating composition can be applied to the porous substrate as a pre-print coating or a post-print coating.