diff --git a/src/libei-device.c b/src/libei-device.c
index 226cacf..8193fc1 100644
--- a/src/libei-device.c
+++ b/src/libei-device.c
@@ -365,6 +365,8 @@ ei_device_start_emulating(struct ei_device *device)
 	if (device->state != EI_DEVICE_STATE_RESUMED)
 		return;
 
+	assert(!device->send_frame_event);
+
 	device->state = EI_DEVICE_STATE_EMULATING;
 	ei_send_start_emulating(device);
 }
diff --git a/src/libeis-device.c b/src/libeis-device.c
index 3e9be58..679009b 100644
--- a/src/libeis-device.c
+++ b/src/libeis-device.c
@@ -325,6 +325,8 @@ eis_device_start_emulating(struct eis_device *device)
 	if (device->state != EIS_DEVICE_STATE_RESUMED)
 		return;
 
+	assert(!device->send_frame_event);
+
 	device->state = EIS_DEVICE_STATE_EMULATING;
 
 	handle_request_noargs(device, start_emulating);