Partisan voters are optimistic about electoral outcomes: their estimates of the probability of electoral success for their party are substantially higher than the average among the electorate. This has large potential implications for political bargaining. Optimistic electoral expectations make costly bargaining delay look more favourable, which may induce partisans to punish their party for agreeing to a compromise rather than waiting, for example by not turning out to vote. Party decision makers should take this into account when bargaining. We set up and analyse a simple game theoretic model to explore the implications of partisan optimism for political bargaining. We show that increased optimism among a partisan group leads to a stronger bargaining position for their party, but may hurt its electoral prospects. Another main finding is that even high levels of partisan optimism do not in themselves cause inefficient bargaining delay.