diff --git a/include/maxscale/dcb.hh b/include/maxscale/dcb.hh
index b731d0bbc..988b6b781 100644
--- a/include/maxscale/dcb.hh
+++ b/include/maxscale/dcb.hh
@@ -189,6 +189,7 @@ struct DCB : public MXB_POLL_DATA
                                                  *      -1: Evicted from the persistent pool and being closed.
                                                  *   non-0: Time when placed in the persistent pool.
                                                  */
+    bool           valid_for_pool = true;       // TODO: Make this private in 2.5
     SERVICE*       service = nullptr;           /**< The related service */
     void*          data = nullptr;              /**< Client protocol data, owned by client DCB */
     void*          authenticator_data = nullptr;/**< The authenticator data for this DCB */
diff --git a/server/core/backend.cc b/server/core/backend.cc
index d95b25299..5467327b5 100644
--- a/server/core/backend.cc
+++ b/server/core/backend.cc
@@ -61,6 +61,7 @@ void Backend::close(close_type type)
             /** Clean operation counter in bref and in SERVER */
             if (is_waiting_result())
             {
+                m_dcb->valid_for_pool = false;
                 clear_state(WAITING_RESULT);
             }
             clear_state(IN_USE);
diff --git a/server/core/dcb.cc b/server/core/dcb.cc
index 31c4c0c26..0a927981f 100644
--- a/server/core/dcb.cc
+++ b/server/core/dcb.cc
@@ -1260,6 +1260,7 @@ static bool dcb_maybe_add_persistent(DCB* dcb)
         && strlen(dcb->user)
         && server
         && dcb->session
+        && dcb->valid_for_pool
         && session_valid_for_pool(dcb->session)
         && server->persistpoolmax()
         && (server->status & SERVER_RUNNING)