diff --git a/coders/mono.c b/coders/mono.c
index 2a17030..8d91544 100644
--- a/coders/mono.c
+++ b/coders/mono.c
@@ -314,7 +314,7 @@
   if (status == MagickFalse)
     return(status);
   if (IsRGBColorspace(image->colorspace) == MagickFalse)
-    (void) TransformImageColorspace(image,RGBColorspace,exception);
+    (void) TransformImageColorspace(image,sRGBColorspace,exception);
   /*
     Convert image to a bi-level image.
   */