German finance minister Wolfgang Schäuble ruled out a coalition between his conservative party and the Social Democrats after September’s election in an interview with Der Spiegel that will be published on Monday, expressing confidence that its alliance with the right-wing liberals will maintain a majority in the lower chamber of parliament.

Although most opinion polls suggest that the liberals will struggle to cross the 5 percent election threshold in the fall, Schäuble warned right-wing voters that his party “won’t form a coalition with anyone” else. “If the right doesn’t win a majority,” he added, the Social Democrats and Green party should “repeat what they did in North Rhine-Westphalia,” Germany’s most populous state where the two left-wing parties fell short of a legislative majority in a state election three years ago but were able to form a government with the backing of the far-left Die Linke.

Even if Die Linke could lose up to half of its seats in the national parliament in September, it might still get enough votes to help the Social Democrats and Greens secure a majority. In a Forsa poll released last week, they got 24 and 13 percent respectively, compared to 41 percent for Chancellor Angela Merkel’s conservatives.

Bündnis 90/Die Grünen, once a far-left pacifist movement, has made itself more electable in recent years with centrist leaders and an emphasis on phasing out nuclear power, widely supported in Germany after the 2011 Fukushima nuclear power plant disaster in Japan. But it lurched left last month when its party conference adopted income and wealth tax hikes. That might drive middle income voters into the arms of the Social Democrats while drawing hard leftists from Die Linke, raising the prospect of a left-wing majority emerging, if at the expense of the Greens’ own rise.

If neither the left nor the right wins an outright majority, as polls predict, it is doubtful that Merkel’s conservatives won’t consider a “grand coalition” with the Social Democrats as they did in 2005.

Merkel has frustrated her current coalition partners by not pursuing a more liberal economic policy while the two major parties are largely agreed on what should be Germany’s policy in Europe. Even the Social Democrats appear slightly more sympathetic toward debtor states in the south, they won’t argue for more flexibility either, rather insist that reforms should be carried out as a condition for international financial aid to which Germany is the main contributor.