diff --git a/PIL/ImageShow.py b/PIL/ImageShow.py
index a0978ab39..f59ba9bad 100644
--- a/PIL/ImageShow.py
+++ b/PIL/ImageShow.py
@@ -117,7 +117,7 @@ elif sys.platform == "darwin":
 
     class MacViewer(Viewer):
         format = "PNG"
-        options = {'compress-level': 1}
+        options = {'compress_level': 1}
 
         def get_command(self, file, **options):
             # on darwin open returns immediately resulting in the temp
@@ -145,7 +145,7 @@ else:
 
     class UnixViewer(Viewer):
         format = "PNG"
-        options = {'compress-level': 1}
+        options = {'compress_level': 1}
 
         def show_file(self, file, **options):
             command, executable = self.get_command_ex(file, **options)