diff --git a/defaults/main.yml b/defaults/main.yml
index 071dd57..1686876 100644
--- a/defaults/main.yml
+++ b/defaults/main.yml
@@ -6,13 +6,13 @@ basesystem_role: workstation
 # basesystem_arch: [i386|amd64|powerpc]
 basesystem_arch: null
 
-basesystem_task_desktop: false
-basesystem_task_development: false
-basesystem_task_multimedia: false
-basesystem_task_network: false
-basesystem_task_office: false
-basesystem_task_security: false
-basesystem_task_shell: false
-basesystem_task_shopping: false
-basesystem_task_system: false
+basesystem_task_desktop: null
+basesystem_task_development: null
+basesystem_task_multimedia: null
+basesystem_task_network: null
+basesystem_task_office: null
+basesystem_task_security: null
+basesystem_task_shell: null
+basesystem_task_shopping: null
+basesystem_task_system: null
 
diff --git a/tasks/development.yml b/tasks/development.yml
index 82eec8f..7764c01 100644
--- a/tasks/development.yml
+++ b/tasks/development.yml
@@ -13,6 +13,7 @@
     - devscripts
     - git-core
     - git-flow
+    - mercurial
     - hg-fast-export
     - libtool
     - meld
diff --git a/tasks/main.yml b/tasks/main.yml
index 3219da4..49ab69d 100644
--- a/tasks/main.yml
+++ b/tasks/main.yml
@@ -1,5 +1,36 @@
 ---
 
+## FIXME: check that default values are sane, or fail
+- fail: Please set basesystem_arch value to something ...
+  when: basesystem_arch == null
+
+- fail: Please set basesystem_task_desktop to either true or false
+  when: basesystem_task_desktop == null
+
+- fail: Please set basesystem_task_development to either true or false
+  when: basesystem_task_development == null
+
+- fail: Please set basesystem_task_multimedia to either true or false
+  when: basesystem_task_multimedia == null
+
+- fail: Please set basesystem_task_network to either true or false
+  when: basesystem_task_network == null
+
+- fail: Please set basesystem_task_office to either true or false
+  when: basesystem_task_office == null
+
+- fail: Please set basesystem_task_security to either true or false
+  when: basesystem_task_security == null
+
+- fail: Please set basesystem_task_shell to either true or false
+  when: basesystem_task_shell == null
+
+- fail: Please set basesystem_task_shopping to either true or false
+  when: basesystem_task_shopping == null
+
+- fail: Please set basesystem_task_system to either true or false
+  when: basesystem_task_system == null
+
 - template: 
     src=apt_conf_glenuxnet_base.j2
     dest=/etc/apt/apt.conf.d/00glenuxnet_base