Does internal debt matter? Japan's yen-denominated public debt now totals 140% of GDP, and this number continues to rise rapidly. What constraints will this growing debt finally encounter? I argue that finance can postpone but not eliminate payments owed by the government to the private sector. The combination of continuing Keynsian budget deficits, bleeding banks, overleveraged municipalities and massive pension liabilities will ultimately bring into question the credibility of the government's many promises. The result could be a massive issuance of new currency.