Frequent app bugs and low tolerance for loss of functionality create an impetus for self-healing smartphone software. We take a step towards this via on-the-fly error detection and automated patching. Specifically, we add failure detection and recovery to Android by detecting crashes and "sealing off" the crashing part of the app to avoid future crashes. In the detection stage, our system dynamically analyzes app execution to detect certain exceptional situations. In the recovery stage, we use bytecode rewriting to alter app behavior as to avoid such situations in the future. When using our implementation, apps can resume operation (albeit with limited functionality) instead of repeatedly crashing. Our approach does not require access to app source code or any system (e.g., kernel-level) modification. Experiments on several real-world, popular Android apps and bugs show that our approach manages to recover the apps from crashes effectively, timely, and without introducing overhead.