diff --git a/query-converter/Design.hs b/query-converter/Design.hs
index 4b546459..e7277c79 100644
--- a/query-converter/Design.hs
+++ b/query-converter/Design.hs
@@ -74,7 +74,7 @@ tex6 = getERDiagram [
 displayER e = do
   writeFile "er-tmp.dot" $ prERDiagram e
   system "fdp -Tpng er-tmp.dot >er-tmp.png" -- dot or neato sometimes better
-  system $ pngviewer os ++ " er-tmp.png"
+  system $ viewer ++ " er-tmp.png"
   putStrLn $ prSchema $ erdiagram2schema SER e  -- only E-R strategy implemented; OO and Null TODO
   putStrLn ""
   putStrLn $ erdiagram2text e
diff --git a/query-converter/QConv.hs b/query-converter/QConv.hs
index 133d3ea8..3b1a1b5f 100644
--- a/query-converter/QConv.hs
+++ b/query-converter/QConv.hs
@@ -117,7 +117,7 @@ alg2latex env s = case pTable (preprocSQL (myLexer s)) of
       "\\end{document}"
       ]
     system "pdflatex qconv-latex-tmp.tex > //dev//null"
-    system $ pdfviewer os ++ " qconv-latex-tmp.pdf"
+    system $ viewer ++ " qconv-latex-tmp.pdf"
     return ()
 
 mintex = "qconv-latex-tmp.tex"
diff --git a/query-converter/Viewer.hs b/query-converter/Viewer.hs
index 46fd84f3..ac2470de 100644
--- a/query-converter/Viewer.hs
+++ b/query-converter/Viewer.hs
@@ -1,15 +1,9 @@
 module Viewer where
 
--- for viewing E-R designs and relational algebra files
-
--- select your OS
-os = "mac"
--- os = "linux"
+import System.Info (os)
 
-pngviewer os = case os of
-  "mac" -> "open"
-  "linux" -> "eog"
+-- for viewing E-R designs and relational algebra files
 
-pdfviewer os = case os of
-  "mac" -> "open"
-  "linux" -> "evince"
+viewer = case os of
+  "darwin" -> "open"
+  "linux"  -> "xdg-open"