diff --git a/bin/canga b/bin/canga
index 1afab9d..7face00 100755
--- a/bin/canga
+++ b/bin/canga
@@ -307,7 +307,7 @@ class Canga < Thor
 
     rc = check.check
 
-    exit(-1) if !rc
+    exit(-1) if rc
   end
 end
 
diff --git a/lib/cangallo/check.rb b/lib/cangallo/check.rb
index 07bba6b..d131ee6 100644
--- a/lib/cangallo/check.rb
+++ b/lib/cangallo/check.rb
@@ -32,7 +32,7 @@ def check
       if problem
         text = <<-EOT
 There is at least one problem in your system. You can go this page to
-get more information on how to fix them:
+get more information on how to fix it:
 
 https://canga.io/install/
 
@@ -41,6 +41,13 @@ def check
         STDERR.puts text
       end
 
+      STDERR.puts <<-EOT
+It's also a good idea to execute libguestfs test tool:
+
+    $ libguestfs-test-tool
+
+EOT
+
       problem
     end