diff --git a/agb-image-converter/src/lib.rs b/agb-image-converter/src/lib.rs
index 139c7aad..1cd8356b 100644
--- a/agb-image-converter/src/lib.rs
+++ b/agb-image-converter/src/lib.rs
@@ -116,8 +116,13 @@ pub fn include_aseprite_inner(input: TokenStream) -> TokenStream {
         for frame in frames {
             let width = frame.width();
             let height = frame.height();
-            assert!(width.is_power_of_two() && width <= 64);
-            assert!(height.is_power_of_two() && height <= 64);
+            assert!(
+                valid_sprite_size(width, height),
+                "File {} contains sprites with unrepresentable size {}x{}",
+                filename.display(),
+                width,
+                height
+            );
 
             let image = Image::load_from_dyn_image(frame);
             add_to_optimiser(&mut optimiser, &image, 8, Some(transparent_colour));
@@ -398,3 +403,21 @@ mod tests {
         assert_eq!(AnimationDirection::PingPong as usize, 2);
     }
 }
+
+fn valid_sprite_size(width: u32, height: u32) -> bool {
+    match (width, height) {
+        (8, 8) => true,
+        (16, 16) => true,
+        (32, 32) => true,
+        (64, 64) => true,
+        (16, 8) => true,
+        (32, 8) => true,
+        (32, 16) => true,
+        (64, 32) => true,
+        (8, 16) => true,
+        (8, 32) => true,
+        (16, 32) => true,
+        (32, 64) => true,
+        (_, _) => false,
+    }
+}