diff --git a/news/403.bugfix b/news/403.bugfix
new file mode 100644
index 000000000..8e35448af
--- /dev/null
+++ b/news/403.bugfix
@@ -0,0 +1 @@
+- Fix installation to preserve existing order of behaviors. [davisagli]
diff --git a/src/plone/app/multilingual/browser/setup.py b/src/plone/app/multilingual/browser/setup.py
index 90d0391ad..230261ac8 100644
--- a/src/plone/app/multilingual/browser/setup.py
+++ b/src/plone/app/multilingual/browser/setup.py
@@ -284,6 +284,6 @@ def ensure_translatable(self, type_):
 
         if IDexterityFTI.providedBy(fti):
             behaviors = list(fti.behaviors)
-            behaviors.append("plone.translatable")
-            behaviors = tuple(set(behaviors))
-            fti._updateProperty("behaviors", behaviors)
+            if "plone.translatable" not in behaviors:
+                behaviors.append("plone.translatable")
+            fti._updateProperty("behaviors", tuple(behaviors))
diff --git a/src/plone/app/multilingual/setuphandlers.py b/src/plone/app/multilingual/setuphandlers.py
index 549edf77b..357325798 100644
--- a/src/plone/app/multilingual/setuphandlers.py
+++ b/src/plone/app/multilingual/setuphandlers.py
@@ -58,14 +58,10 @@ def enable_translatable_behavior(portal):
     )
     for fti in dx_ftis:
         # Enable translatable behavior for all types
-        behaviors = list(fti.behaviors)
-        behaviors.extend(
-            [
-                "plone.translatable",
-            ]
-        )
-        behaviors = tuple(set(behaviors))
-        fti._updateProperty("behaviors", behaviors)
+        if "plone.translatable" not in fti.behaviors:
+            behaviors = list(fti.behaviors)
+            behaviors.append("plone.translatable")
+            fti._updateProperty("behaviors", tuple(behaviors))
 
 
 def step_uninstall_various(context):