diff --git a/changelogs/fragments/hash_behaviour_inventory.yml b/changelogs/fragments/hash_behaviour_inventory.yml
new file mode 100644
index 00000000000..d289bba9520
--- /dev/null
+++ b/changelogs/fragments/hash_behaviour_inventory.yml
@@ -0,0 +1,2 @@
+bugfixes:
+    - Inventory sources now respect setting ``hash_behaviour``. Previously each new inventory source would overwrite existing vars, even when ``hash_behavior`` was set to ``merge``.
diff --git a/docs/docsite/rst/porting_guides/porting_guide_2.9.rst b/docs/docsite/rst/porting_guides/porting_guide_2.9.rst
index 9c25696b57f..d63a38b59c5 100644
--- a/docs/docsite/rst/porting_guides/porting_guide_2.9.rst
+++ b/docs/docsite/rst/porting_guides/porting_guide_2.9.rst
@@ -19,7 +19,7 @@ This document is part of a collection on porting. The complete list of porting g
 Playbook
 ========
 
-No notable changes
+ * ``hash_behaviour`` now affects inventory sources. If you have it set to ``merge``, the data you get from inventory might change and you will have to update playbooks accordingly. If you're using the default setting (``overwrite``), you will see no changes. Inventory was ignoring this setting.
 
 
 Command Line
diff --git a/lib/ansible/inventory/group.py b/lib/ansible/inventory/group.py
index 6d5e19ef592..4d1d6ab0d6c 100644
--- a/lib/ansible/inventory/group.py
+++ b/lib/ansible/inventory/group.py
@@ -22,8 +22,9 @@ from itertools import chain
 from ansible import constants as C
 from ansible.errors import AnsibleError
 from ansible.module_utils._text import to_native, to_text
-
+from ansible.module_utils.common._collections_compat import Mapping, MutableMapping
 from ansible.utils.display import Display
+from ansible.utils.vars import combine_vars
 
 display = Display()
 
@@ -245,7 +246,10 @@ class Group:
         if key == 'ansible_group_priority':
             self.set_priority(int(value))
         else:
-            self.vars[key] = value
+            if key in self.vars and isinstance(self.vars[key], MutableMapping) and isinstance(value, Mapping):
+                self.vars[key] = combine_vars(self.vars[key], value)
+            else:
+                self.vars[key] = value
 
     def clear_hosts_cache(self):
 
diff --git a/lib/ansible/inventory/host.py b/lib/ansible/inventory/host.py
index 43272739454..91bb5570b0a 100644
--- a/lib/ansible/inventory/host.py
+++ b/lib/ansible/inventory/host.py
@@ -20,6 +20,7 @@ from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
 from ansible.inventory.group import Group
+from ansible.module_utils.common._collections_compat import Mapping, MutableMapping
 from ansible.utils.vars import combine_vars, get_unique_id
 
 __all__ = ['Host']
@@ -137,7 +138,10 @@ class Host:
                         self.remove_group(oldg)
 
     def set_variable(self, key, value):
-        self.vars[key] = value
+        if key in self.vars and isinstance(self.vars[key], MutableMapping) and isinstance(value, Mapping):
+            self.vars[key] = combine_vars(self.vars[key], value)
+        else:
+            self.vars[key] = value
 
     def get_groups(self):
         return self.groups