diff --git a/wgengine/magicsock/magicsock.go b/wgengine/magicsock/magicsock.go
index be3633f12..398803faf 100644
--- a/wgengine/magicsock/magicsock.go
+++ b/wgengine/magicsock/magicsock.go
@@ -3941,6 +3941,10 @@ func (c *Conn) UpdateNetmapDelta(muts []netmap.NodeMutation) {
 			ep.mu.Unlock()
 		}
 	}
+
+	// As of 2026-06-11 we will only get deltas from the control plane, so upon
+	// receiving one we should infer we have switched out of the cached state.
+	c.usingCachedNetmap.Store(false)
 }
 
 // UpdateStatus implements the interface needed by ipnstate.StatusBuilder.