diff --git a/changelog/11433.bugfix.md b/changelog/11433.bugfix.md
new file mode 100644
index 000000000000..852540d098ed
--- /dev/null
+++ b/changelog/11433.bugfix.md
@@ -0,0 +1 @@
+This fix makes sure that when a Domain object is loaded from multiple files where one file specifies a custom session config and the rest do not, the default session configuration does not override the custom session config.
diff --git a/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/config.yml b/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/config.yml
new file mode 100644
index 000000000000..6e9195534e75
--- /dev/null
+++ b/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/config.yml
@@ -0,0 +1,39 @@
+recipe: default.v1
+language: en
+pipeline: []
+# # No configuration for the NLU pipeline was provided. The following default pipeline was used to train your model.
+# # If you'd like to customize it, uncomment and adjust the pipeline.
+# # See https://rasa.com/docs/rasa/tuning-your-model for more information.
+#   - name: WhitespaceTokenizer
+#   - name: RegexFeaturizer
+#   - name: LexicalSyntacticFeaturizer
+#   - name: CountVectorsFeaturizer
+#   - name: CountVectorsFeaturizer
+#     analyzer: char_wb
+#     min_ngram: 1
+#     max_ngram: 4
+#   - name: DIETClassifier
+#     epochs: 100
+#     constrain_similarities: true
+#   - name: EntitySynonymMapper
+#   - name: ResponseSelector
+#     epochs: 100
+#     constrain_similarities: true
+#   - name: FallbackClassifier
+#     threshold: 0.3
+#     ambiguity_threshold: 0.1
+
+data:
+policies:
+# # No configuration for policies was provided. The following default policies were used to train your model.
+# # If you'd like to customize them, uncomment and adjust the policies.
+# # See https://rasa.com/docs/rasa/policies for more information.
+#   - name: MemoizationPolicy
+#   - name: RulePolicy
+#   - name: UnexpecTEDIntentPolicy
+#     max_history: 5
+#     epochs: 100
+#   - name: TEDPolicy
+#     max_history: 5
+#     epochs: 100
+#     constrain_similarities: true
diff --git a/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/data/nlu.yml b/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/data/nlu.yml
new file mode 100644
index 000000000000..2f6c3f8c7d3e
--- /dev/null
+++ b/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/data/nlu.yml
@@ -0,0 +1,91 @@
+version: "3.1"
+
+nlu:
+- intent: greet
+  examples: |
+    - hey
+    - hello
+    - hi
+    - hello there
+    - good morning
+    - good evening
+    - moin
+    - hey there
+    - let's go
+    - hey dude
+    - goodmorning
+    - goodevening
+    - good afternoon
+
+- intent: goodbye
+  examples: |
+    - cu
+    - good by
+    - cee you later
+    - good night
+    - bye
+    - goodbye
+    - have a nice day
+    - see you around
+    - bye bye
+    - see you later
+
+- intent: affirm
+  examples: |
+    - yes
+    - y
+    - indeed
+    - of course
+    - that sounds good
+    - correct
+
+- intent: deny
+  examples: |
+    - no
+    - n
+    - never
+    - I don't think so
+    - don't like that
+    - no way
+    - not really
+
+- intent: mood_great
+  examples: |
+    - perfect
+    - great
+    - amazing
+    - feeling like a king
+    - wonderful
+    - I am feeling very good
+    - I am great
+    - I am amazing
+    - I am going to save the world
+    - super stoked
+    - extremely good
+    - so so perfect
+    - so good
+    - so perfect
+
+- intent: mood_unhappy
+  examples: |
+    - my day was horrible
+    - I am sad
+    - I don't feel very well
+    - I am disappointed
+    - super sad
+    - I'm so sad
+    - sad
+    - very sad
+    - unhappy
+    - not good
+    - not very good
+    - extremly sad
+    - so saad
+    - so sad
+
+- intent: bot_challenge
+  examples: |
+    - are you a bot?
+    - are you a human?
+    - am I talking to a bot?
+    - am I talking to a human?
diff --git a/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/data/responses.yml b/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/data/responses.yml
new file mode 100644
index 000000000000..03929b32bf11
--- /dev/null
+++ b/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/data/responses.yml
@@ -0,0 +1,6 @@
+version: "3.1"
+
+
+responses:
+  utter_test:
+  - text: "Hey! How are you?"
diff --git a/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/data/stories.yml b/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/data/stories.yml
new file mode 100644
index 000000000000..6ff78ee20864
--- /dev/null
+++ b/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/data/stories.yml
@@ -0,0 +1,30 @@
+version: "3.1"
+
+stories:
+
+- story: happy path
+  steps:
+  - intent: greet
+  - action: utter_greet
+  - intent: mood_great
+  - action: utter_happy
+
+- story: sad path 1
+  steps:
+  - intent: greet
+  - action: utter_greet
+  - intent: mood_unhappy
+  - action: utter_cheer_up
+  - action: utter_did_that_help
+  - intent: affirm
+  - action: utter_happy
+
+- story: sad path 2
+  steps:
+  - intent: greet
+  - action: utter_greet
+  - intent: mood_unhappy
+  - action: utter_cheer_up
+  - action: utter_did_that_help
+  - intent: deny
+  - action: utter_goodbye
diff --git a/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/domain.yml b/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/domain.yml
new file mode 100644
index 000000000000..751380631360
--- /dev/null
+++ b/data/test_domains/test_domain_files_with_no_session_config_and_custom_session_config/domain.yml
@@ -0,0 +1,34 @@
+version: "3.1"
+
+intents:
+  - greet
+  - goodbye
+  - affirm
+  - deny
+  - mood_great
+  - mood_unhappy
+  - bot_challenge
+
+responses:
+  utter_greet:
+  - text: "Hey! How are you?"
+
+  utter_cheer_up:
+  - text: "Here is something to cheer you up:"
+    image: "https://i.imgur.com/nGF1K8f.jpg"
+
+  utter_did_that_help:
+  - text: "Did that help you?"
+
+  utter_happy:
+  - text: "Great, carry on!"
+
+  utter_goodbye:
+  - text: "Bye"
+
+  utter_iamabot:
+  - text: "I am a bot, powered by Rasa."
+
+session_config:
+  session_expiration_time: 0
+  carry_over_slots_to_new_session: false
diff --git a/rasa/shared/core/domain.py b/rasa/shared/core/domain.py
index 4ab90f46768e..4ccbe8b1d4b5 100644
--- a/rasa/shared/core/domain.py
+++ b/rasa/shared/core/domain.py
@@ -339,7 +339,10 @@ def merge_domain_dicts(
             override
             or combined.get(SESSION_CONFIG_KEY) == SessionConfig.default().as_dict()
             or combined.get(SESSION_CONFIG_KEY) is None
-        ) and domain_dict.get(SESSION_CONFIG_KEY):
+        ) and domain_dict.get(SESSION_CONFIG_KEY) not in [
+            None,
+            SessionConfig.default().as_dict(),
+        ]:
             combined[SESSION_CONFIG_KEY] = domain_dict[SESSION_CONFIG_KEY]
 
         # remove existing forms from new actions
diff --git a/tests/regressions/test_domain_merge_multiple_files_with_custom_session_config_and_no_session_config.py b/tests/regressions/test_domain_merge_multiple_files_with_custom_session_config_and_no_session_config.py
new file mode 100644
index 000000000000..a224b1341461
--- /dev/null
+++ b/tests/regressions/test_domain_merge_multiple_files_with_custom_session_config_and_no_session_config.py
@@ -0,0 +1,40 @@
+from rasa.shared.core.domain import SessionConfig
+from rasa.shared.importers.importer import TrainingDataImporter
+
+
+def test_merge_domain_with_custom_session_config_and_no_session_config():
+    expected_session_expiration_time = 0
+    expected_carry_over_slots = False
+
+    config_path = (
+        "data/test_domains/"
+        "test_domain_files_with_no_session_config_and_custom_session_config/config.yml"
+    )
+    domain_path = (
+        "data/test_domains/"
+        "test_domain_files_with_no_session_config_and_custom_session_config/domain.yml"
+    )
+    training_data_paths = [
+        "data/test_domains/"
+        "test_domain_files_with_no_session_config_and_custom_session_config/data"
+    ]
+    file_importer = TrainingDataImporter.load_from_config(
+        config_path, domain_path, training_data_paths
+    )
+
+    domain = file_importer.get_domain()
+
+    assert (
+        domain.session_config.session_expiration_time
+        != SessionConfig.default().session_expiration_time
+    )
+    assert (
+        domain.session_config.carry_over_slots
+        != SessionConfig.default().carry_over_slots
+    )
+
+    assert (
+        domain.session_config.session_expiration_time
+        == expected_session_expiration_time
+    )
+    assert domain.session_config.carry_over_slots == expected_carry_over_slots