diff --git a/libfprint/drivers/aes1610.c b/libfprint/drivers/aes1610.c
index c9742e9..0326565 100644
--- a/libfprint/drivers/aes1610.c
+++ b/libfprint/drivers/aes1610.c
@@ -710,7 +710,6 @@ capture_sm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
     {
       start_finger_detection (dev);
     }
-  fpi_ssm_free (ssm);
 }
 
 static void
@@ -774,7 +773,6 @@ activate_sm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
 
   if (!error)
     start_finger_detection (dev);
-  fpi_ssm_free (ssm);
 }
 
 static void
diff --git a/libfprint/drivers/aes2501.c b/libfprint/drivers/aes2501.c
index fad0218..1b59c56 100644
--- a/libfprint/drivers/aes2501.c
+++ b/libfprint/drivers/aes2501.c
@@ -575,7 +575,6 @@ capture_sm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
     {
       start_finger_detection (dev);
     }
-  fpi_ssm_free (ssm);
 }
 
 static void
@@ -806,7 +805,6 @@ activate_sm_complete (FpiSsm *ssm, FpDevice *dev, GError *error)
 
   if (!error)
     start_finger_detection (FP_IMAGE_DEVICE (dev));
-  fpi_ssm_free (ssm);
 }
 
 static void
diff --git a/libfprint/drivers/aes2550.c b/libfprint/drivers/aes2550.c
index 2abcf76..b95b053 100644
--- a/libfprint/drivers/aes2550.c
+++ b/libfprint/drivers/aes2550.c
@@ -391,7 +391,6 @@ capture_sm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
     {
       start_finger_detection (dev);
     }
-  fpi_ssm_free (ssm);
 }
 
 static void
@@ -537,7 +536,6 @@ activate_sm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
 
   if (!error)
     start_finger_detection (dev);
-  fpi_ssm_free (ssm);
 }
 
 static void
diff --git a/libfprint/drivers/aesx660.c b/libfprint/drivers/aesx660.c
index 8ad4c63..3f13252 100644
--- a/libfprint/drivers/aesx660.c
+++ b/libfprint/drivers/aesx660.c
@@ -215,7 +215,6 @@ finger_det_sm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
 
   fp_dbg ("Finger detection completed");
   fpi_image_device_report_finger_status (dev, TRUE);
-  fpi_ssm_free (ssm);
 
   if (priv->deactivating)
     {
@@ -466,7 +465,6 @@ capture_sm_complete (FpiSsm *ssm, FpDevice *device, GError *error)
   FpiDeviceAesX660Private *priv = fpi_device_aes_x660_get_instance_private (self);
 
   fp_dbg ("Capture completed");
-  fpi_ssm_free (ssm);
 
   if (priv->deactivating)
     {
@@ -672,7 +670,6 @@ static void
 activate_sm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
 {
   fpi_image_device_activate_complete (FP_IMAGE_DEVICE (_dev), error);
-  fpi_ssm_free (ssm);
 
   if (!error)
     start_finger_detection (FP_IMAGE_DEVICE (_dev));
diff --git a/libfprint/drivers/elan.c b/libfprint/drivers/elan.c
index 961366e..5e80be5 100644
--- a/libfprint/drivers/elan.c
+++ b/libfprint/drivers/elan.c
@@ -479,7 +479,6 @@ stop_capture_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
 
   G_DEBUG_HERE ();
 
-  fpi_ssm_free (ssm);
 
   /* The device is inactive at this point. */
   self->dev_state = FP_IMAGE_DEVICE_STATE_INACTIVE;
@@ -606,7 +605,6 @@ capture_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
       fpi_image_device_session_error (dev, error);
     }
 
-  fpi_ssm_free (ssm);
 }
 
 static void
@@ -789,7 +787,6 @@ calibrate_complete (FpiSsm *ssm, FpDevice *dev, GError *error)
       elan_capture (dev);
     }
 
-  fpi_ssm_free (ssm);
 }
 
 static void
@@ -886,7 +883,6 @@ activate_complete (FpiSsm *ssm, FpDevice *dev, GError *error)
 
   fpi_image_device_activate_complete (idev, error);
 
-  fpi_ssm_free (ssm);
 }
 
 static void
diff --git a/libfprint/drivers/etes603.c b/libfprint/drivers/etes603.c
index 5c990da..55f0139 100644
--- a/libfprint/drivers/etes603.c
+++ b/libfprint/drivers/etes603.c
@@ -789,7 +789,6 @@ m_exit_complete (FpiSsm *ssm, FpDevice *dev, GError *error)
   else
     fp_dbg ("The device is now in idle state");
   fpi_image_device_deactivate_complete (idev, error);
-  fpi_ssm_free (ssm);
 }
 
 static void
@@ -911,7 +910,6 @@ m_capture_complete (FpiSsm *ssm, FpDevice *dev, GError *error)
           g_error_free (error);
         }
     }
-  fpi_ssm_free (ssm);
 
   if (self->is_active == TRUE)
     {
@@ -1061,7 +1059,6 @@ m_finger_complete (FpiSsm *ssm, FpDevice *dev, GError *error)
       self->is_active = FALSE;
     }
 
-  fpi_ssm_free (ssm);
 }
 
 static void
@@ -1265,7 +1262,6 @@ m_tunevrb_complete (FpiSsm *ssm, FpDevice *dev, GError *error)
   if (!self->is_active)
     m_exit_start (idev);
 
-  fpi_ssm_free (ssm);
 }
 
 /*
@@ -1409,7 +1405,6 @@ m_tunedc_complete (FpiSsm *ssm, FpDevice *dev, GError *error)
   if (!self->is_active)
     m_exit_start (idev);
 
-  fpi_ssm_free (ssm);
 }
 
 static void
@@ -1543,7 +1538,6 @@ m_init_complete (FpiSsm *ssm, FpDevice *dev, GError *error)
       reset_param (FPI_DEVICE_ETES603 (dev));
       fpi_image_device_session_error (idev, error);
     }
-  fpi_ssm_free (ssm);
 }
 
 static void
diff --git a/libfprint/drivers/synaptics/synaptics.c b/libfprint/drivers/synaptics/synaptics.c
index a2286b2..4932d01 100644
--- a/libfprint/drivers/synaptics/synaptics.c
+++ b/libfprint/drivers/synaptics/synaptics.c
@@ -290,7 +290,6 @@ cmd_ssm_done (FpiSsm *ssm, FpDevice *dev, GError *error)
     }
   self->cmd_complete_on_removal = FALSE;
   g_clear_pointer (&self->cmd_complete_error, g_error_free);
-  fpi_ssm_free (ssm);
 }
 
 static void
diff --git a/libfprint/drivers/upeksonly.c b/libfprint/drivers/upeksonly.c
index ec81375..e1cd7e5 100644
--- a/libfprint/drivers/upeksonly.c
+++ b/libfprint/drivers/upeksonly.c
@@ -1380,7 +1380,6 @@ loopsm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
   FpImageDevice *dev = FP_IMAGE_DEVICE (_dev);
   FpiDeviceUpeksonly *self = FPI_DEVICE_UPEKSONLY (_dev);
 
-  fpi_ssm_free (ssm);
 
   if (self->deactivating)
     {
@@ -1401,7 +1400,6 @@ initsm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
   FpImageDevice *dev = FP_IMAGE_DEVICE (_dev);
   FpiDeviceUpeksonly *self = FPI_DEVICE_UPEKSONLY (_dev);
 
-  fpi_ssm_free (ssm);
   fpi_image_device_activate_complete (dev, error);
   if (error)
     return;
diff --git a/libfprint/drivers/upektc.c b/libfprint/drivers/upektc.c
index ff5b49b..e1254ce 100644
--- a/libfprint/drivers/upektc.c
+++ b/libfprint/drivers/upektc.c
@@ -157,7 +157,6 @@ activate_sm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
 
   if (!error)
     start_finger_detection (dev);
-  fpi_ssm_free (ssm);
 }
 
 
@@ -345,7 +344,6 @@ capture_sm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
   else
     start_finger_detection (dev);
 
-  fpi_ssm_free (ssm);
 }
 
 static void
diff --git a/libfprint/drivers/upektc_img.c b/libfprint/drivers/upektc_img.c
index 1e06b90..28a709f 100644
--- a/libfprint/drivers/upektc_img.c
+++ b/libfprint/drivers/upektc_img.c
@@ -389,7 +389,6 @@ capture_sm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error_arg)
 
   g_autoptr(GError) error = error_arg;
 
-  fpi_ssm_free (ssm);
 
   /* Note: We assume that the error is a cancellation in the deactivation case */
   if (self->deactivating)
@@ -470,7 +469,6 @@ deactivate_sm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
   FpiDeviceUpektcImg *self = FPI_DEVICE_UPEKTC_IMG (_dev);
 
   fp_dbg ("Deactivate completed");
-  fpi_ssm_free (ssm);
 
   self->deactivating = FALSE;
   fpi_image_device_deactivate_complete (dev,  error);
@@ -601,7 +599,6 @@ activate_sm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
 {
   FpImageDevice *dev = FP_IMAGE_DEVICE (_dev);
 
-  fpi_ssm_free (ssm);
   fpi_image_device_activate_complete (dev, error);
 
   if (!error)
diff --git a/libfprint/drivers/upekts.c b/libfprint/drivers/upekts.c
index b3481aa..4bc6556 100644
--- a/libfprint/drivers/upekts.c
+++ b/libfprint/drivers/upekts.c
@@ -990,7 +990,6 @@ enroll_stop_deinit_cb (FpiSsm *ssm, FpDevice *dev, GError *error)
     fp_warn ("Error deinitializing: %s", error->message);
 
   fpi_device_enroll_complete (dev, data->print, data->error);
-  fpi_ssm_free (ssm);
 }
 
 static void
@@ -1217,7 +1216,6 @@ enroll_started (FpiSsm *ssm, FpDevice *dev, GError *error)
   else
     enroll_iterate (dev);
 
-  fpi_ssm_free (ssm);
 }
 
 static void
@@ -1256,7 +1254,6 @@ verify_stop_deinit_cb (FpiSsm *ssm, FpDevice *dev, GError *error)
     fp_warn ("Error deinitializing: %s", error->message);
 
   fpi_device_verify_complete (dev, data->res, NULL, data->error);
-  fpi_ssm_free (ssm);
 }
 
 static void
@@ -1540,7 +1537,6 @@ verify_started (FpiSsm *ssm, FpDevice *dev, GError *error)
   upekdev->first_verify_iteration = TRUE;
   verify_iterate (dev);
 
-  fpi_ssm_free (ssm);
 }
 
 static void
diff --git a/libfprint/drivers/uru4000.c b/libfprint/drivers/uru4000.c
index f248411..89328d0 100644
--- a/libfprint/drivers/uru4000.c
+++ b/libfprint/drivers/uru4000.c
@@ -789,7 +789,6 @@ imaging_complete (FpiSsm *ssm, FpDevice *dev, GError *error)
 {
   FpiDeviceUru4000 *self = FPI_DEVICE_URU4000 (dev);
 
-  fpi_ssm_free (ssm);
 
   /* Report error before exiting imaging loop - the error handler
    * can request state change, which needs to be postponed to end of
diff --git a/libfprint/drivers/vcom5s.c b/libfprint/drivers/vcom5s.c
index 0e10252..edd2dd4 100644
--- a/libfprint/drivers/vcom5s.c
+++ b/libfprint/drivers/vcom5s.c
@@ -301,7 +301,6 @@ loopsm_complete (FpiSsm *ssm, FpDevice *dev, GError *error)
   FpImageDevice *imgdev = FP_IMAGE_DEVICE (dev);
   FpDeviceVcom5s *self = FPI_DEVICE_VCOM5S (dev);
 
-  fpi_ssm_free (ssm);
   g_object_unref (self->capture_img);
   self->capture_img = NULL;
   self->loop_running = FALSE;
diff --git a/libfprint/drivers/vfs0050.c b/libfprint/drivers/vfs0050.c
index 4dc6782..1be272b 100644
--- a/libfprint/drivers/vfs0050.c
+++ b/libfprint/drivers/vfs0050.c
@@ -669,7 +669,6 @@ dev_activate_callback (FpiSsm *ssm, FpDevice *dev, GError *error)
       g_error_free (error);
     }
 
-  fpi_ssm_free (ssm);
 }
 
 /* Activate device */
@@ -710,7 +709,6 @@ dev_open_callback (FpiSsm *ssm, FpDevice *dev, GError *error)
 {
   /* Notify open complete */
   fpi_image_device_open_complete (FP_IMAGE_DEVICE (dev), error);
-  fpi_ssm_free (ssm);
 }
 
 /* Open device */
diff --git a/libfprint/drivers/vfs101.c b/libfprint/drivers/vfs101.c
index 37e083c..9ca1b0a 100644
--- a/libfprint/drivers/vfs101.c
+++ b/libfprint/drivers/vfs101.c
@@ -960,7 +960,6 @@ m_loop_complete (FpiSsm *ssm, FpDevice *dev, GError *error)
 
   self->active = FALSE;
 
-  fpi_ssm_free (ssm);
 }
 
 /* Init ssm states */
@@ -1268,7 +1267,6 @@ m_init_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
     }
 
   /* Free sequential state machine */
-  fpi_ssm_free (ssm);
 }
 
 /* Activate device */
diff --git a/libfprint/drivers/vfs301.c b/libfprint/drivers/vfs301.c
index 8fdac7c..7219792 100644
--- a/libfprint/drivers/vfs301.c
+++ b/libfprint/drivers/vfs301.c
@@ -168,7 +168,6 @@ m_loop_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
       g_error_free (error);
     }
   /* Free sequential state machine */
-  fpi_ssm_free (ssm);
 }
 
 /* Exec init sequential state machine */
@@ -201,7 +200,6 @@ m_init_complete (FpiSsm *ssm, FpDevice *dev, GError *error)
     }
 
   /* Free sequential state machine */
-  fpi_ssm_free (ssm);
 }
 
 /* Activate device */
diff --git a/libfprint/drivers/vfs5011.c b/libfprint/drivers/vfs5011.c
index 9eddca7..007e486 100644
--- a/libfprint/drivers/vfs5011.c
+++ b/libfprint/drivers/vfs5011.c
@@ -745,7 +745,6 @@ activate_loop_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
       submit_image (ssm, self, dev);
       fpi_image_device_report_finger_status (dev, FALSE);
     }
-  fpi_ssm_free (ssm);
 
   self->loop_running = FALSE;
 
@@ -793,7 +792,6 @@ open_loop_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
   self->init_sequence.receive_buf = NULL;
 
   fpi_image_device_open_complete (dev, error);
-  fpi_ssm_free (ssm);
 }
 
 static void
diff --git a/libfprint/fpi-ssm.c b/libfprint/fpi-ssm.c
index 1569be8..a614860 100644
--- a/libfprint/fpi-ssm.c
+++ b/libfprint/fpi-ssm.c
@@ -51,6 +51,7 @@
  *
  * To start a ssm, you pass in a completion callback function to fpi_ssm_start()
  * which gets called when the ssm completes (both on error and on failure).
+ * Starting a ssm also takes ownership of it.
  *
  * To iterate to the next state, call fpi_ssm_next_state(). It is legal to
  * attempt to iterate beyond the final state - this is equivalent to marking
@@ -58,6 +59,7 @@
  *
  * To mark successful completion of a SSM, either iterate beyond the final
  * state or call fpi_ssm_mark_completed() from any state.
+ * This will also invalidate the machine, freeing it.
  *
  * To mark failed completion of a SSM, call fpi_ssm_mark_failed() from any
  * state. You must pass a non-zero error code.
@@ -125,7 +127,6 @@ fpi_ssm_new (FpDevice             *dev,
  * @ssm_data_destroy: (nullable): #GDestroyNotify for @ssm_data
  *
  * Sets @machine's data (freeing the existing data, if any).
- *
  */
 void
 fpi_ssm_set_data (FpiSsm        *machine,
@@ -182,12 +183,16 @@ __ssm_call_handler (FpiSsm *machine)
 
 /**
  * fpi_ssm_start:
- * @ssm: an #FpiSsm state machine
+ * @ssm: (transfer full): an #FpiSsm state machine
  * @callback: the #FpiSsmCompletedCallback callback to call on completion
  *
  * Starts a state machine. You can also use this function to restart
  * a completed or failed state machine. The @callback will be called
  * on completion.
+ *
+ * Note that @ssm will be stolen when this function is called.
+ * So that all associated data will be free'ed automatically, after the
+ * @callback is ran.
  */
 void
 fpi_ssm_start (FpiSsm *ssm, FpiSsmCompletedCallback callback)
@@ -210,7 +215,6 @@ __subsm_complete (FpiSsm *ssm, FpDevice *_dev, GError *error)
     fpi_ssm_mark_failed (parent, error);
   else
     fpi_ssm_next_state (parent);
-  fpi_ssm_free (ssm);
 }
 
 /**
@@ -253,6 +257,7 @@ fpi_ssm_mark_completed (FpiSsm *machine)
 
       machine->callback (machine, machine->dev, error);
     }
+  fpi_ssm_free (machine);
 }
 
 /**
@@ -260,7 +265,7 @@ fpi_ssm_mark_completed (FpiSsm *machine)
  * @machine: an #FpiSsm state machine
  * @error: a #GError
  *
- * Mark a state machine as failed with @error as the error code.
+ * Mark a state machine as failed with @error as the error code, completing it.
  */
 void
 fpi_ssm_mark_failed (FpiSsm *machine, GError *error)
@@ -305,6 +310,8 @@ fpi_ssm_next_state (FpiSsm *machine)
  * @state: the state to jump to
  *
  * Jump to the @state state, bypassing intermediary states.
+ * If @state is the last state, the machine won't be completed unless
+ * fpi_ssm_mark_completed() isn't explicitly called.
  */
 void
 fpi_ssm_jump_to_state (FpiSsm *machine, int state)