diff --git a/hals/keymaster/KeymasterDevice.cpp b/hals/keymaster/KeymasterDevice.cpp
index e56590d..d616b3b 100644
--- a/hals/keymaster/KeymasterDevice.cpp
+++ b/hals/keymaster/KeymasterDevice.cpp
@@ -114,6 +114,17 @@
     return return_value;
 }
 
+// Helper class to call a finalizer on stack unwind.
+class Finalize {
+ private:
+    std::function<void()> f_;
+
+ public:
+    Finalize(std::function<void()> f) : f_(f) {}
+    ~Finalize() { if (f_) f_(); }
+    void release() { f_ = {}; }
+};
+
 }  // namespace
 
 // std
@@ -553,6 +564,8 @@
     uint64_t operationHandle = startResponse.handle().handle();
     ContinueAttestKeyRequest continueRequest;
     ContinueAttestKeyResponse continueResponse;
+    // Prepare to abort the pending operation in event of an error.
+    Finalize finalize([&] () { abort(operationHandle); });
 
     continueRequest.mutable_handle()->set_handle(operationHandle);
     // TODO
@@ -588,6 +601,7 @@
     // verify cert chain
 
     _hidl_cb(ErrorCode::OK, hidl_vec<hidl_vec<uint8_t> >(chain));
+    finalize.release();
     return Void();
 }