It was a much-needed cold shower, a reality check for the Conservative Eurosceptics who thought Angela Merkel would arrive for her high-profile visit to London bearing gifts for them.
Instead, the German Chancellor brought them crashing down to earth by making clear Britain would have no chance of persuading the other 27 members of the EU club to fundamentally rewrite its rules. Some limited changes - yes. A special deal for the UK alone - no. That was her message.
It will disappoint hardline Tory Europhobes, who are already threatening to make the PM's life hell if he retains power at next year's general election and fails to bring back a range of powers from Brussels to Westminster.
Mrs Merkel spoke of a “step by step” approach, not the “big bang” the Eurosceptics dream about. This makes Mr Cameron's goal to negotiate a new deal for Britain in time for an in/out referendum in 2017 look highly ambitious. He might yet have to delay it. His game of 28-dimensional chess could take longer.
The German Chancellor wants to keep the UK in the EU - but not at any price. She will advise Mr Cameron not to threaten to walk out if he doesn't get his way. As one German source put it: “We will keep open the door for Britain. But you have to walk through it.”