We construct a post-Keynesian public capital accumulation model with a target public debt ratio. Our model elucidates the relationships between economic growth, stability, and fiscal fragility based on Minsky’s classification of hedge, speculative, and Ponzi financing. The main conclusions are as follows: First, steady-state stability requires the Keynesian stability condition, the Domar stability condition, and a positive labour productivity growth rate. Second, policy coordination between the government and central bank is important for preventing fiscal fragility during high economic growth. Third, there are three cases of fiscal fragility and stability. For high economic growth, stability, and fiscal consolidation targets, it is preferable to have the hedging position stable. Finally, our model shows that there may be a threshold for the public debt ratio above which economic growth slows down, but the threshold is neither unique nor universal.