diff --git a/src/ucp/proto/proto_am.inl b/src/ucp/proto/proto_am.inl
index 3c2d18ea31b..779fcbea032 100644
--- a/src/ucp/proto/proto_am.inl
+++ b/src/ucp/proto/proto_am.inl
@@ -345,11 +345,14 @@ ucs_status_t ucp_do_am_zcopy_multi(uct_pending_req_t *self, uint8_t am_id_first,
 
     if (enable_am_bw && (req->send.state.dt.offset != 0)) {
         req->send.lane = ucp_send_request_get_am_bw_lane(req);
-        ucp_send_request_add_reg_lane(req, req->send.lane);
     } else {
         req->send.lane = ucp_ep_get_am_lane(ep);
     }
 
+    if (enable_am_bw || (req->send.state.dt.offset == 0)) {
+        ucp_send_request_add_reg_lane(req, req->send.lane);
+    }
+
     uct_ep     = ep->uct_eps[req->send.lane];
     max_middle = ucp_ep_get_max_zcopy(ep, req->send.lane) - hdr_size_middle;
     max_iov    = ucp_ep_get_max_iov(ep, req->send.lane);
diff --git a/src/ucs/datastruct/callbackq.c b/src/ucs/datastruct/callbackq.c
index 7a9c97d0fc1..4d5e558c042 100644
--- a/src/ucs/datastruct/callbackq.c
+++ b/src/ucs/datastruct/callbackq.c
@@ -363,18 +363,20 @@ static unsigned ucs_callbackq_slow_proxy(void *arg)
 {
     ucs_callbackq_t      *cbq  = arg;
     ucs_callbackq_priv_t *priv = ucs_callbackq_priv(cbq);
+    unsigned num_slow_elems    = priv->num_slow_elems;
+    unsigned count             = 0;
     ucs_callbackq_elem_t *elem;
     unsigned UCS_V_UNUSED removed_idx;
     unsigned slow_idx, fast_idx;
     ucs_callbackq_elem_t tmp_elem;
-    unsigned count = 0;
 
     ucs_trace_poll("cbq=%p", cbq);
 
     ucs_callbackq_enter(cbq);
 
-    /* Execute and update slow-path callbacks */
-    for (slow_idx = 0; slow_idx < priv->num_slow_elems; ++slow_idx) {
+    /* Execute and update slow-path callbacks by num_slow_elems copy to avoid
+     * infinite loop if callback adds another one */
+    for (slow_idx = 0; slow_idx < num_slow_elems; ++slow_idx) {
         elem = &priv->slow_elems[slow_idx];
         if (elem->id == UCS_CALLBACKQ_ID_NULL) {
             continue;
diff --git a/test/gtest/ucs/test_callbackq.cc b/test/gtest/ucs/test_callbackq.cc
index 705dbdc9134..c8e840d4616 100644
--- a/test/gtest/ucs/test_callbackq.cc
+++ b/test/gtest/ucs/test_callbackq.cc
@@ -32,6 +32,7 @@ class test_callbackq :
         uint32_t                  count;
         int                       command;
         callback_ctx              *to_add;
+        unsigned                  flags;
         int                       key;
     };
 
@@ -81,9 +82,11 @@ class test_callbackq :
     void init_ctx(callback_ctx *ctx, int key = 0)
     {
         ctx->test        = this;
+        ctx->callback_id = UCS_CALLBACKQ_ID_NULL;
         ctx->count       = 0;
         ctx->command     = COMMAND_NONE;
-        ctx->callback_id = UCS_CALLBACKQ_ID_NULL;
+        ctx->to_add      = NULL;
+        ctx->flags       = 0;
         ctx->key         = key;
     }
 
@@ -95,7 +98,7 @@ class test_callbackq :
     {
         ctx->callback_id = ucs_callbackq_add(&m_cbq, callback_proxy,
                                              reinterpret_cast<void*>(ctx),
-                                             cb_flags() | flags);
+                                             ctx->flags | cb_flags() | flags);
     }
 
     void remove(int callback_id)
@@ -215,19 +218,22 @@ UCS_TEST_P(test_callbackq, add_another) {
     ctx.command = COMMAND_NONE;
 
     unsigned count = ctx.count;
+    if (cb_flags() & UCS_CALLBACKQ_FLAG_FAST) {
+        count++; /* fast CBs are executed immediately after "add" */
+    }
 
     dispatch();
     EXPECT_EQ(2u, ctx.count);
-    EXPECT_EQ(count + 1, ctx2.count);
+    EXPECT_EQ(count, ctx2.count);
 
     remove(&ctx);
     dispatch();
     EXPECT_EQ(2u, ctx.count);
-    EXPECT_EQ(count + 2, ctx2.count);
+    EXPECT_EQ(count + 1, ctx2.count);
 
     remove(&ctx2);
     dispatch();
-    EXPECT_EQ(count + 2, ctx2.count);
+    EXPECT_EQ(count + 1, ctx2.count);
 }
 
 UCS_MT_TEST_P(test_callbackq, threads, 10) {
@@ -337,6 +343,24 @@ UCS_TEST_F(test_callbackq_noflags, oneshot) {
     EXPECT_EQ(1u, ctx.count);
 }
 
+UCS_TEST_F(test_callbackq_noflags, oneshot_recursive) {
+    callback_ctx ctx;
+
+    init_ctx(&ctx);
+    ctx.command = COMMAND_ADD_ANOTHER;
+    ctx.flags   = UCS_CALLBACKQ_FLAG_ONESHOT;
+    ctx.to_add  = &ctx;
+
+    add(&ctx);
+
+    for (unsigned i = 0; i < 10; ++i) {
+        dispatch(1);
+        EXPECT_LE(i + 1, ctx.count);
+    }
+
+    remove(ctx.callback_id);
+}
+
 UCS_TEST_F(test_callbackq_noflags, remove_if) {
     const size_t count = 1000;
     const int num_keys = 10;