Purpose:　Collaborative　projects　require　overlapping　skills　and　capabilities　to　facilitate　knowledge　transfer.　However,　not　all　kinds　of　learning　are　virtuous　and　some　may　lead　to　leakage　of　commercially　valuable　knowledge.　The　purpose　of　this　paper　is　to　explain　and　restrain　leakage　of　organizational　competitive　knowledge　in　collaborative　projects.　Design/methodology/approach:　A　total　of　398　survey　questionnaires　are　collected　from　project-based　firms　in　Pakistan.　We　gathered　data　from　horizontal　and　vertical　collaborations.　Analysis　is　conducted　with　transaction　cost　economics　lens　through　Process　Macro　3.0.　Findings:　Findings　suggest　that　partner’s　learning　intent　(PLI)　and　distrust　positively　affect　knowledge　leakage,　whereas　human　resource　management　(HRM)　practices　have　negative　effect　on　knowledge　leakage.　Furthermore,　HRM　practices　negatively　moderate　the　relationship　between　PLI　and　knowledge　leakage　and　distrust　positively　mediates　it.　Research　limitations/implications:　This　study　integrates　HRM　with　knowledge　management　to　restrain　knowledge　leakage　and　contributes　to　knowledge　management　and　strategic　management.　This　study　examines　knowledge　leakage　in　the　presence　of　passive　opportunism.　Originality/value:　This　study　explains　how　passive　opportunism　translates　into　opportunistic　behavior.　Besides,　effectiveness　of　HRM　practices　are　least　surveyed　to　restrain　passive　and　active　opportunisms.　©　2022,　Emerald　Publishing　Limited.