Dallas Federal Reserve President Richard Fisher, who has long criticized the central bank’s bond-buying stimulus, says the program has lasted too long and there are signs it is now distorting financial markets and encouraging risk-taking.

In a speech in Mexico City Wednesday, Fisher highlighted concerns that the Fed’s policy stimulus is creating asset-price bubbles that “may result in tears” for investors acting on bad incentives.

“There are increasing signs quantitative easing has overstayed its welcome: Market distortions and acting on bad incentives are becoming more pervasive,” Fisher told the Association of Mexican Banks.

“I fear that we are feeding imbalances similar to those that played a role in the run-up to the financial crisis.

The Fed has bought more than $3 trillion in Treasury and mortgage-based bonds since late 2008 to lower longer-term borrowing costs and stimulate hiring and growth.

Although new Fed Chairman Janet Yellen has started to taper its asset-buying program, which now amounts to $65 billion a month, Fisher said he is still concerned that the stimulus has encouraged investors to take risks that could destabilize markets.

He pointed to soaring margin debt margin and the narrow spreads between corporate and Treasury debt as concerns.

“We must monitor these indicators very carefully so as to ensure that the ghost of ‘irrational exuberance’ does not haunt us again.”