diff --git a/src/containerapp/HISTORY.rst b/src/containerapp/HISTORY.rst
index 0cc57231005..b926b479f51 100644
--- a/src/containerapp/HISTORY.rst
+++ b/src/containerapp/HISTORY.rst
@@ -8,9 +8,9 @@ Release History
 * Added parameter --environment to 'az containerapp list'
 * Added 'az containerapp revision label swap' to swap traffic labels
 * BREAKING CHANGE: 'az containerapp revision list' now shows only active revisions by default, added flag --all to show all revisions
+* Fixed but with 'az containerapp up' where custom domains would be removed when updating existing containerapp
 * Fixed bug with 'az containerapp auth update' when using --unauthenticated-client-action
 
-
 0.3.5
 ++++++
 * Add parameter --zone-redundant to 'az containerapp env create'
diff --git a/src/containerapp/azext_containerapp/custom.py b/src/containerapp/azext_containerapp/custom.py
index 86aaebba9f5..9f638f3238a 100644
--- a/src/containerapp/azext_containerapp/custom.py
+++ b/src/containerapp/azext_containerapp/custom.py
@@ -2344,7 +2344,10 @@ def containerapp_up_logic(cmd, resource_group_name, name, managed_env, image, en
 
     ingress_def = None
     if target_port is not None and ingress is not None:
-        ingress_def = IngressModel
+        if ca_exists:
+            ingress_def = containerapp_def["properties"]["configuration"]["ingress"]
+        else:
+            ingress_def = IngressModel
         ingress_def["external"] = external_ingress
         ingress_def["targetPort"] = target_port
         containerapp_def["properties"]["configuration"]["ingress"] = ingress_def