diff --git a/src/xpra/client/gobject_client_base.py b/src/xpra/client/gobject_client_base.py
index 8a55030d19..6e578252bd 100644
--- a/src/xpra/client/gobject_client_base.py
+++ b/src/xpra/client/gobject_client_base.py
@@ -122,7 +122,7 @@ def __init__(self, opts):
         #don't bother with many of these things for one-off commands:
         for x in ("ui_client", "wants_aliases", "wants_encodings",
                   "wants_versions", "wants_features", "wants_sound", "windows",
-                  "webcam",
+                  "webcam", "keyboard", "mouse",
                   ):
             self.hello_extra[x] = False
 
diff --git a/src/xpra/client/ui_client_base.py b/src/xpra/client/ui_client_base.py
index 3f8d870a4e..b0b71afdf4 100644
--- a/src/xpra/client/ui_client_base.py
+++ b/src/xpra/client/ui_client_base.py
@@ -352,6 +352,7 @@ def make_hello(self):
             "share"                     : self.client_supports_sharing,
             "lock"                      : self.client_lock,
             })
+        caps.update({"mouse" : True})
         caps.update(self.get_keyboard_caps())
         for c in CLIENT_BASES:
             caps.update(c.get_caps(self))
diff --git a/src/xpra/server/source/input_mixin.py b/src/xpra/server/source/input_mixin.py
index cf65b374dc..5c412613b3 100644
--- a/src/xpra/server/source/input_mixin.py
+++ b/src/xpra/server/source/input_mixin.py
@@ -18,6 +18,12 @@
 """
 class InputMixin(StubSourceMixin):
 
+    @classmethod
+    def is_needed(cls, caps : typedict) -> bool:
+        #the 'input' capability was only added in v4,
+        #so we have to enable the mixin by default:
+        return caps.boolget("keyboard", True) or caps.boolget("mouse", True)
+
     def init_state(self):
         self.pointer_relative = False
         self.keyboard_config = None