diff --git a/displayarray/frame/frame_updater.py b/displayarray/frame/frame_updater.py
index 52aa0a8..b76d68a 100644
--- a/displayarray/frame/frame_updater.py
+++ b/displayarray/frame/frame_updater.py
@@ -54,7 +54,11 @@ class FrameUpdater(threading.Thread):
                     frame_c = c(frame)
                     if frame_c is not None:
                         frame = frame_c
-                if frame.shape[-1] not in [1, 3] and len(frame.shape) != 2:
+                if (
+                    isinstance(frame, np.ndarray)
+                    and frame.shape[-1] not in [1, 3]
+                    and len(frame.shape) != 2
+                ):
                     print(
                         f"Too many channels in output. (Got {frame.shape[-1]} instead of 1 or 3.) "
                         f"Frame selection callback added."
diff --git a/displayarray/window/subscriber_windows.py b/displayarray/window/subscriber_windows.py
index 89c9504..19768cd 100644
--- a/displayarray/window/subscriber_windows.py
+++ b/displayarray/window/subscriber_windows.py
@@ -146,7 +146,8 @@ class SubscriberWindows(object):
             if isinstance(self.frames[f], Exception):
                 raise self.frames[f]
             if (
-                self.frames[f].shape[-1] not in [1, 3]
+                isinstance(self.frames[f], np.ndarray)
+                and self.frames[f].shape[-1] not in [1, 3]
                 and len(self.frames[f].shape) != 2
             ):
                 print(