diff --git a/src/networking.cpp b/src/networking.cpp
index 1cb9eade6..6ff41d1ab 100644
--- a/src/networking.cpp
+++ b/src/networking.cpp
@@ -2779,6 +2779,7 @@ NULL
             != C_OK) return;
         struct client *target = lookupClientByID(id);
         if (target && target->flags & CLIENT_BLOCKED) {
+            std::unique_lock<fastlock> ul(target->lock);
             if (unblock_error)
                 addReplyError(target,
                     "-UNBLOCKED client unblocked via CLIENT UNBLOCK");