diff --git a/modules/txt2img.py b/modules/txt2img.py
index 6e79ebd5..516d4a7f 100644
--- a/modules/txt2img.py
+++ b/modules/txt2img.py
@@ -58,11 +58,18 @@ def txt2img_create_processing(id_task: str, request: gr.Request, prompt: str, ne
 
 def txt2img_upscale_function(id_task: str, request: gr.Request, gallery, gallery_index, generation_info, *args):
     assert len(gallery) > 0, 'No image to upscale'
-    assert 0 <= gallery_index < len(gallery), f'Bad image index: {gallery_index}'
+
+    if gallery_index < 0 or gallery_index >= len(gallery):
+        return gallery, generation_info, f'Bad image index: {gallery_index}', ''
+
+    geninfo = json.loads(generation_info)
 
     #   catch situation where user tries to hires-fix the grid: probably a mistake, results can be bad aspect ratio - just don't do it
-    if opts.return_grid and 0 == gallery_index and len(gallery) > 1:
-        return gallery, generation_info, 'Unable to upscale the grid image.', ''
+    first_image_index = geninfo.get('index_of_first_image', 0)
+    #   catch if user tries to upscale a control image, this function will fail later trying to get infotext that doesn't exist
+    count_images = len(geninfo.get('infotexts'))        #   note: we have batch_size in geninfo, but not batch_count
+    if len(gallery) > 1 and (gallery_index < first_image_index or gallery_index >= count_images):
+        return gallery, generation_info, 'Unable to upscale grid or control images.', ''
 
     p = txt2img_create_processing(id_task, request, *args, force_enable_hr=True)
     p.batch_size = 1
@@ -70,8 +77,6 @@ def txt2img_upscale_function(id_task: str, request: gr.Request, gallery, gallery
     # txt2img_upscale attribute that signifies this is called by txt2img_upscale
     p.txt2img_upscale = True
 
-    geninfo = json.loads(generation_info)
-
     image_info = gallery[gallery_index]
     p.firstpass_image = infotext_utils.image_from_url_text(image_info)