diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index 3827ab09d..1a8c59bc0 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -2698,7 +2698,7 @@ def open(fp, mode="r"):
         raise ValueError("bad mode %r" % mode)
     elif isinstance(fp, io.StringIO):
         raise ValueError(
-            "StringIO cannot be used to open an image. Binary data must be used instead"
+            "StringIO cannot be used to open an image. Binary data must be used instead."
         )
 
     exclusive_fp = False