diff --git a/src/PIL/ImageFont.py b/src/PIL/ImageFont.py
index ef4527782..77d2cf0f9 100644
--- a/src/PIL/ImageFont.py
+++ b/src/PIL/ImageFont.py
@@ -865,7 +865,7 @@ class TransposedFont:
 
     def getlength(self, text, *args, **kwargs):
         if self.orientation in (Image.Transpose.ROTATE_90, Image.Transpose.ROTATE_270):
-            raise ValueError("text length is undefined for rotated text")
+            raise ValueError("text length is undefined for text rotated by 90 or 270 degrees")
         return self.font.getlength(text, *args, **kwargs)