diff --git a/wagtail/images/blocks.py b/wagtail/images/blocks.py
index ca1b3d2169..dc9378c677 100644
--- a/wagtail/images/blocks.py
+++ b/wagtail/images/blocks.py
@@ -148,16 +148,9 @@ class ImageBlock(StructBlock):
     def bulk_to_python(self, values):
         values = list(values)
 
-        # The normal case: `values` is a list of dicts. This is the normal representation of this block.
-        if all(isinstance(value, dict) for value in values):
-            # `values` is a list of dicts containing `image`, `decorative` and `alt_text` keys
-            struct_values = super().bulk_to_python(values)
-
-        # Else we are in a fallback for backwards compatibility with ImageChooserBlock
-        else:
-            # `values` might be a list of image IDs (as we might encounter if an ImageChooserBlock has been
-            # changed to an ImageBlock with no data migration)
-            # Or it could be a [None] if we are coming from an empty ImageChooserBlock
+        if values and all(value is None or isinstance(value, int) for value in values):
+            # `values` looks like a list of image IDs and/or None values (as we might encounter
+            # if an ImageChooserBlock has been changed to an ImageBlock with no data migration)
             image_values = self.child_blocks["image"].bulk_to_python(values)
 
             struct_values = [
@@ -169,6 +162,12 @@ class ImageBlock(StructBlock):
                 for image in image_values
             ]
 
+        else:
+            # Treat `values` as the standard ImageBlock representation - a (possibly empty) list of
+            # dicts containing `image`, `decorative` and `alt_text` keys to be handled by the
+            # StructBlock superclass
+            struct_values = super().bulk_to_python(values)
+
         return [
             self._struct_value_to_image(struct_value) for struct_value in struct_values
         ]