diff --git a/gtk/src/toga_gtk/images.py b/gtk/src/toga_gtk/images.py
index 74928047cb..cf8534d1d5 100644
--- a/gtk/src/toga_gtk/images.py
+++ b/gtk/src/toga_gtk/images.py
@@ -29,7 +29,8 @@ def get_data(self):
         success, buffer = self.native.save_to_bufferv("png")
         if success:
             return buffer
-        else:
+        else:  # pragma: nocover
+            # This shouldn't ever happen, and it's difficult to manufacture in test conditions
             raise ValueError("Unable to get PNG data for image")
 
     def save(self, path):
diff --git a/gtk/src/toga_gtk/window.py b/gtk/src/toga_gtk/window.py
index 120ab9b69b..32589bebfd 100644
--- a/gtk/src/toga_gtk/window.py
+++ b/gtk/src/toga_gtk/window.py
@@ -184,5 +184,6 @@ def get_image_data(self):
         success, buffer = screenshot.save_to_bufferv("png")
         if success:
             return buffer
-        else:
+        else:  # pragma: nocover
+            # This shouldn't ever happen, and it's difficult to manufacture in test conditions
             raise ValueError(f"Unable to generate screenshot of {self}")