diff --git a/Tests/test_image.py b/Tests/test_image.py
index ade9d03c980..3c2d128ee73 100644
--- a/Tests/test_image.py
+++ b/Tests/test_image.py
@@ -94,7 +94,7 @@ def test_open_formats(self):
         with pytest.raises(TypeError):
             Image.open(PNGFILE, formats=123)
 
-        for formats in [["JPEG"], ("JPEG",)]:
+        for formats in [["JPEG"], ("JPEG",), ["jpeg"], ["Jpeg"], ["jPeG"], ["JpEg"]]:
             with pytest.raises(UnidentifiedImageError):
                 Image.open(PNGFILE, formats=formats)
 
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index e6d3adcf748..01fe7ed1bae 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -2922,6 +2922,7 @@ def open(fp, mode="r", formats=None):
 
     def _open_core(fp, filename, prefix, formats):
         for i in formats:
+            i = i.upper()
             if i not in OPEN:
                 init()
             try: