diff --git a/changelogs/fragments/inv_available_hosts_to_frozenset.yml b/changelogs/fragments/inv_available_hosts_to_frozenset.yml
new file mode 100644
index 00000000000..094fe6ddd54
--- /dev/null
+++ b/changelogs/fragments/inv_available_hosts_to_frozenset.yml
@@ -0,0 +1,2 @@
+bugfixes:
+  - ansible-inventory - index available_hosts for major performance boost when dumping large inventories
\ No newline at end of file
diff --git a/lib/ansible/cli/inventory.py b/lib/ansible/cli/inventory.py
index 448214cee43..3550079bf8e 100755
--- a/lib/ansible/cli/inventory.py
+++ b/lib/ansible/cli/inventory.py
@@ -325,7 +325,7 @@ class InventoryCLI(CLI):
             return results
 
         hosts = self.inventory.get_hosts(top.name)
-        results = format_group(top, [h.name for h in hosts])
+        results = format_group(top, frozenset(h.name for h in hosts))
 
         # populate meta
         results['_meta'] = {'hostvars': {}}
@@ -381,7 +381,7 @@ class InventoryCLI(CLI):
 
             return results
 
-        available_hosts = [h.name for h in self.inventory.get_hosts(top.name)]
+        available_hosts = frozenset(h.name for h in self.inventory.get_hosts(top.name))
         return format_group(top, available_hosts)
 
     def toml_inventory(self, top):
@@ -425,7 +425,7 @@ class InventoryCLI(CLI):
 
             return results
 
-        available_hosts = [h.name for h in self.inventory.get_hosts(top.name)]
+        available_hosts = frozenset(h.name for h in self.inventory.get_hosts(top.name))
         results = format_group(top, available_hosts)
 
         return results