diff --git a/tasks/set_vars.yml b/tasks/set_vars.yml
index 7051f2097c..d9c61e8826 100644
--- a/tasks/set_vars.yml
+++ b/tasks/set_vars.yml
@@ -1,11 +1,9 @@
 ---
 - name: Ensure ansible_facts used by role
   setup:
-    gather_subset:
-      - min
-      - hardware
-  when: not ansible_facts.keys() | list |
-    intersect(__postgresql_required_facts) == __postgresql_required_facts
+    gather_subset: "{{ __postgresql_required_facts_subsets }}"
+  when: __postgresql_required_facts |
+    difference(ansible_facts.keys() | list) | length > 0
 
 - name: Set platform/version specific variables
   include_vars: "{{ __vars_file }}"
diff --git a/vars/main.yml b/vars/main.yml
index 87972e7a11..e1db07fb40 100644
--- a/vars/main.yml
+++ b/vars/main.yml
@@ -23,3 +23,12 @@ __postgresql_required_facts:
   - distribution_version
   - os_family
   - ansible_memory_mb
+
+# these facts cannot be used as a gather_subset
+__postgresql_no_subset_facts: [ansible_memory_mb]
+
+# the subsets of ansible_facts that need to be gathered in case any of the
+# facts in required_facts is missing; see the documentation of
+# the 'gather_subset' parameter of the 'setup' module
+__postgresql_required_facts_subsets: "{{ ['!all', '!min', 'hardware'] +
+  __postgresql_required_facts | difference(__postgresql_no_subset_facts) }}"