I analyse whether coalitions consisting of one or several parties from both political blocs have a causal effect on the following election results of the Sweden Democrats using election data. I find that, when the largest bloc is unable to reach a seat majority in a municipal assembly and forms a coalition with one or several parties from the other bloc, the Sweden Democrats increase their municipal vote share by on average 11.71 percentage points the following election. I interpret the result as support for the view that Swedish voters punish the established parties when they are perceived as becoming more similar in terms of policy and ideology. Moreover, my results show that the effect is only significant in municipalities where no small and/or local parties exist, indicating that the largest bloc in many municipalities prefer to form a coalition with these parties when the opportunity exists.