diff --git a/django/db/models/functions/comparison.py b/django/db/models/functions/comparison.py
index c897fc262f..76ef5d219b 100644
--- a/django/db/models/functions/comparison.py
+++ b/django/db/models/functions/comparison.py
@@ -162,7 +162,8 @@ class JSONObject(Func):
 
     def join(self, args):
         pairs = zip(args[::2], args[1::2], strict=True)
-        return ", ".join([" VALUE ".join(pair) for pair in pairs])
+        # Wrap 'key' in parentheses in case of postgres cast :: syntax.
+        return ", ".join([f"({key}) VALUE {value}" for key, value in pairs])
 
     def as_native(self, compiler, connection, *, returning, **extra_context):
         return self.as_sql(
@@ -174,24 +175,28 @@ class JSONObject(Func):
         )
 
     def as_postgresql(self, compiler, connection, **extra_context):
-        if (
-            not connection.features.is_postgresql_16
-            or connection.features.uses_server_side_binding
-        ):
-            copy = self.copy()
-            copy.set_source_expressions(
-                [
-                    Cast(expression, TextField()) if index % 2 == 0 else expression
-                    for index, expression in enumerate(copy.get_source_expressions())
-                ]
+        # Casting keys to text is only required when using JSONB_BUILD_OBJECT
+        # or when using JSON_OBJECT on PostgreSQL 16+ with server-side bindings.
+        # This is done in all cases for consistency.
+        copy = self.copy()
+        copy.set_source_expressions(
+            [
+                Cast(expression, TextField()) if index % 2 == 0 else expression
+                for index, expression in enumerate(copy.get_source_expressions())
+            ]
+        )
+
+        if connection.features.is_postgresql_16:
+            return copy.as_native(
+                compiler, connection, returning="JSONB", **extra_context
             )
-            return super(JSONObject, copy).as_sql(
-                compiler,
-                connection,
-                function="JSONB_BUILD_OBJECT",
-                **extra_context,
-            )
-        return self.as_native(compiler, connection, returning="JSONB", **extra_context)
+
+        return super(JSONObject, copy).as_sql(
+            compiler,
+            connection,
+            function="JSONB_BUILD_OBJECT",
+            **extra_context,
+        )
 
     def as_oracle(self, compiler, connection, **extra_context):
         return self.as_native(compiler, connection, returning="CLOB", **extra_context)