The economics profession seems to increasingly endorse the existence of a strongly negative nonlinear effect of public debt on economic growth. Reinhart and Rogoff (2010) were the first to point out that a public debt-to-GDP ratio higher than 90% of GDP is associated with considerably lower economic performance in advanced and emerging economies alike. A string of recent empirical papers broadly validates this threshold value. This paper seeks to contribute to this literature by putting a variant of the Reinhart-Rogoff dataset to a formal econometric testing. Using nonlinear threshold models, there is some evidence in favour of a negative nonlinear relationship between debt and growth. But these results are very sensitive to the time dimension and country coverage considered, data frequency (annual data vs. multi-year averages) and assumptions on the minimum number of observations required in each nonlinear regime. In addition, we also show that nonlinear effects can kick in at much lower levels of public debt (between 20% and 60% of GDP). These results, based on bivariate regressions on secular time series, are largely confirmed on a shorter dataset (1960-2010) when using a multivariate growth framework that accounts for traditional drivers of long-term economic growth and model uncertainty. Nonlinear effects might be more complex and difficult to model than previously thought. Instability might be a result of nonlinear effects changing over time, across countries and economic conditions. Further research is certainly needed to fully understand the link between public debt and growth.