diff --git a/ompi/mca/coll/acoll/coll_acoll_allgather.c b/ompi/mca/coll/acoll/coll_acoll_allgather.c
index bb7ccf5bbf8..f0e2110402f 100644
--- a/ompi/mca/coll/acoll/coll_acoll_allgather.c
+++ b/ompi/mca/coll/acoll/coll_acoll_allgather.c
@@ -268,6 +268,9 @@ static inline int mca_coll_acoll_allgather_intra(const void *sbuf, int scount,
         data_blk_size[0] = bcount * (num_sgs - 2) + last_subgrp_rcnt;
         blk_ofst[0] = bcount;
     } else if (sg_id == num_sgs - 1) {
+        if (last_subgrp_size < 2) {
+            return err;
+        }
         num_data_blks = 1;
         data_blk_size[0] = bcount * (num_sgs - 1);
         blk_ofst[0] = 0;
@@ -329,8 +332,7 @@ int mca_coll_acoll_allgather(const void *sbuf, int scount, struct ompi_datatype_
     int i;
     int err;
     int size;
-    int rank, adj_rank;
-    int num_sgs;
+    int rank;
     int sg_size, log2_sg_size;
     int num_nodes, node_start, node_end, node_id;
     int node_size, last_node_size;
@@ -388,7 +390,9 @@ int mca_coll_acoll_allgather(const void *sbuf, int scount, struct ompi_datatype_
     if (size <= 2) {
         intra_comm = comm;
     } else {
-        assert(subc->local_r_comm != NULL);
+        if (num_nodes > 1) {
+            assert(subc->local_r_comm != NULL);
+        }
         intra_comm = num_nodes == 1 ? comm : subc->local_r_comm;
     }
     err = mca_coll_acoll_allgather_intra(sbuf, scount, sdtype, local_rbuf, rcount, rdtype,
@@ -454,12 +458,14 @@ int mca_coll_acoll_allgather(const void *sbuf, int scount, struct ompi_datatype_
     } /* End of if inter leader */
 
     /* Do intra node broadcast */
-    num_sgs = (node_size + sg_size - 1) >> log2_sg_size;
     if (node_id == 0) {
         num_data_blks = 1;
         data_blk_size[0] = bcount * (num_nodes - 2) + last_subgrp_rcnt;
         blk_ofst[0] = bcount;
     } else if (node_id == num_nodes - 1) {
+        if (last_node_size < 2) {
+            return err;
+        }
         num_data_blks = 1;
         data_blk_size[0] = bcount * (num_nodes - 1);
         blk_ofst[0] = 0;
diff --git a/ompi/mca/coll/acoll/coll_acoll_barrier.c b/ompi/mca/coll/acoll/coll_acoll_barrier.c
index a07900d7503..06a9ef070d7 100644
--- a/ompi/mca/coll/acoll/coll_acoll_barrier.c
+++ b/ompi/mca/coll/acoll/coll_acoll_barrier.c
@@ -125,7 +125,6 @@ static int mca_coll_acoll_barrier_send_subc(struct ompi_communicator_t *comm,
 int mca_coll_acoll_barrier_intra(struct ompi_communicator_t *comm, mca_coll_base_module_t *module)
 {
     int size, ssize, bsize;
-    int srank;
     int err = MPI_SUCCESS;
     int nreqs = 0;
     ompi_request_t **reqs;
@@ -141,6 +140,9 @@ int mca_coll_acoll_barrier_intra(struct ompi_communicator_t *comm, mca_coll_base
 
     subc = &acoll_module->subc[cid];
     size = ompi_comm_size(comm);
+    if (size == 1) {
+        return err;
+    }
     if (!subc->initialized && size > 1) {
         err = mca_coll_acoll_comm_split_init(comm, acoll_module, 0);
         if (MPI_SUCCESS != err) {
diff --git a/ompi/mca/coll/acoll/coll_acoll_bcast.c b/ompi/mca/coll/acoll/coll_acoll_bcast.c
index 38eb185695d..39bbb73f56e 100644
--- a/ompi/mca/coll/acoll/coll_acoll_bcast.c
+++ b/ompi/mca/coll/acoll/coll_acoll_bcast.c
@@ -37,7 +37,7 @@ static int bcast_binomial(void *buff, int count, struct ompi_datatype_t *datatyp
                           struct ompi_communicator_t *comm, ompi_request_t **preq, int *nreqs,
                           int world_rank)
 {
-    int msb_pos, sub_rank, peer, err;
+    int msb_pos, sub_rank, peer, err = MPI_SUCCESS;
     int size, rank, dim;
     int i, mask;
 
@@ -83,7 +83,7 @@ static int bcast_flat_tree(void *buff, int count, struct ompi_datatype_t *dataty
                            int world_rank)
 {
     int peer;
-    int err;
+    int err = MPI_SUCCESS;
     int rank = ompi_comm_rank(comm);
     int size = ompi_comm_size(comm);
 
diff --git a/ompi/mca/coll/acoll/coll_acoll_gather.c b/ompi/mca/coll/acoll/coll_acoll_gather.c
index f8a0ecc319b..31897f43777 100644
--- a/ompi/mca/coll/acoll/coll_acoll_gather.c
+++ b/ompi/mca/coll/acoll/coll_acoll_gather.c
@@ -43,17 +43,16 @@ int mca_coll_acoll_gather_intra(const void *sbuf, int scount, struct ompi_dataty
     int i, err, rank, size;
     char *wkg = NULL, *workbuf = NULL;
     MPI_Status status;
-    MPI_Aint incr, extent, lb;
     MPI_Aint sextent, sgap = 0, ssize;
-    MPI_Aint rextent, rgap = 0, rsize;
+    MPI_Aint rextent;
     int total_recv = 0;
     int sg_cnt, node_cnt;
     int cur_sg, root_sg;
     int cur_node, root_node;
     int is_base, is_local_root;
     int startr, endr, inc;
-    int startn, endn, incn;
-    int num_nodes, node_id;
+    int startn, endn;
+    int num_nodes;
     mca_coll_acoll_module_t *acoll_module = (mca_coll_acoll_module_t *) module;
     coll_acoll_reserve_mem_t *reserve_mem_gather = &(acoll_module->reserve_mem_s);
 
@@ -70,17 +69,13 @@ int mca_coll_acoll_gather_intra(const void *sbuf, int scount, struct ompi_dataty
         num_nodes = 1;
     }
 
-    ompi_datatype_get_extent(rdtype, &lb, &extent);
-    incr = extent * (ptrdiff_t) rcount;
-
-    /* Setup root for reveive */
+    /* Setup root for receive */
     if (rank == root) {
         ompi_datatype_type_extent(rdtype, &rextent);
-        rsize = opal_datatype_span(&rdtype->super, (int64_t) rcount * size, &rgap);
         /* Just use the recv buffer */
         wkg = (char *) rbuf;
         if (sbuf != MPI_IN_PLACE) {
-            MPI_Aint root_ofst = extent * (ptrdiff_t) (rcount * root);
+            MPI_Aint root_ofst = rextent * (ptrdiff_t) (rcount * root);
             err = ompi_datatype_sndrcv((void *) sbuf, scount, sdtype, wkg + (ptrdiff_t) root_ofst,
                                        rcount, rdtype);
             if (MPI_SUCCESS != err) {
@@ -100,7 +95,7 @@ int mca_coll_acoll_gather_intra(const void *sbuf, int scount, struct ompi_dataty
     is_local_root = (rank % node_cnt == 0) && (cur_node != root_node);
     startn = (rank / node_cnt) * node_cnt;
 
-    if (is_base || (rank == root)) {
+    if (is_base) {
         int64_t buf_size = is_local_root ? (int64_t) scount * node_cnt : (int64_t) scount * sg_cnt;
         ompi_datatype_type_extent(sdtype, &sextent);
         ssize = opal_datatype_span(&sdtype->super, buf_size, &sgap);
@@ -111,7 +106,7 @@ int mca_coll_acoll_gather_intra(const void *sbuf, int scount, struct ompi_dataty
                 return OMPI_ERR_OUT_OF_RESOURCE;
             }
             wkg = workbuf - sgap;
-            tmprecv = wkg + extent * (ptrdiff_t) (rcount * (rank - startr));
+            tmprecv = wkg + sextent * (ptrdiff_t) (rcount * (rank - startr));
             /* local copy to workbuf */
             err = ompi_datatype_sndrcv((void *) sbuf, scount, sdtype, tmprecv, scount, sdtype);
             if (MPI_SUCCESS != err) {
@@ -123,7 +118,7 @@ int mca_coll_acoll_gather_intra(const void *sbuf, int scount, struct ompi_dataty
         rcount = scount;
         rextent = sextent;
         total_recv = rcount;
-    } else {
+    } else if (rank != root) {
         wkg = (char *) sbuf;
         total_recv = scount;
     }
@@ -141,9 +136,9 @@ int mca_coll_acoll_gather_intra(const void *sbuf, int scount, struct ompi_dataty
                 continue;
             }
             if (rank == root) {
-                tmprecv = wkg + extent * (ptrdiff_t) (rcount * i);
+                tmprecv = wkg + rextent * (ptrdiff_t) (rcount * i);
             } else {
-                tmprecv = wkg + extent * (ptrdiff_t) (rcount * (i - startr));
+                tmprecv = wkg + rextent * (ptrdiff_t) (rcount * (i - startr));
             }
             err = MCA_PML_CALL(
                 recv(tmprecv, rcount, rdtype, i, MCA_COLL_BASE_TAG_GATHER, comm, &status));
@@ -161,10 +156,9 @@ int mca_coll_acoll_gather_intra(const void *sbuf, int scount, struct ompi_dataty
     if (endn > size) {
         endn = size;
     }
-    incn = (rank == root) ? ((root != startn) ? 0 : sg_cnt) : sg_cnt;
     if (sg_cnt < size) {
         int local_root = (root_node == cur_node) ? root : startn;
-        for (i = startn + incn; i < endn; i += sg_cnt) {
+        for (i = startn; i < endn; i += sg_cnt) {
             int i_sg = i / sg_cnt;
             if ((rank != local_root) && (rank == i) && is_base) {
                 err = MCA_PML_CALL(send(workbuf - sgap, total_recv, sdtype, local_root,
@@ -173,7 +167,7 @@ int mca_coll_acoll_gather_intra(const void *sbuf, int scount, struct ompi_dataty
             }
             if ((rank == local_root) && (rank != i) && (i_sg != root_sg)) {
                 int recv_amt = (i + sg_cnt > size) ? rcount * (size - i) : rcount * sg_cnt;
-                MPI_Aint rcv_ofst = extent * (ptrdiff_t) (rcount * (i - startn));
+                MPI_Aint rcv_ofst = rextent * (ptrdiff_t) (rcount * (i - startn));
 
                 err = MCA_PML_CALL(recv(wkg + (ptrdiff_t) rcv_ofst, recv_amt, rdtype, i,
                                         MCA_COLL_BASE_TAG_GATHER, comm, &status));
@@ -189,7 +183,7 @@ int mca_coll_acoll_gather_intra(const void *sbuf, int scount, struct ompi_dataty
     }
 
     /* All local roots ranks send to root */
-    if (node_cnt < size) {
+    if (node_cnt < size && num_nodes > 1) {
         for (i = 0; i < size; i += node_cnt) {
             int i_node = i / node_cnt;
             if ((rank != root) && (rank == i) && is_base) {
@@ -199,7 +193,7 @@ int mca_coll_acoll_gather_intra(const void *sbuf, int scount, struct ompi_dataty
             }
             if ((rank == root) && (rank != i) && (i_node != root_node)) {
                 int recv_amt = (i + node_cnt > size) ? rcount * (size - i) : rcount * node_cnt;
-                MPI_Aint rcv_ofst = extent * (ptrdiff_t) (rcount * i);
+                MPI_Aint rcv_ofst = rextent * (ptrdiff_t) (rcount * i);
 
                 err = MCA_PML_CALL(recv((char *) rbuf + (ptrdiff_t) rcv_ofst, recv_amt, rdtype, i,
                                         MCA_COLL_BASE_TAG_GATHER, comm, &status));
diff --git a/ompi/mca/coll/acoll/coll_acoll_module.c b/ompi/mca/coll/acoll/coll_acoll_module.c
index d35a9db94df..9a60d086931 100644
--- a/ompi/mca/coll/acoll/coll_acoll_module.c
+++ b/ompi/mca/coll/acoll/coll_acoll_module.c
@@ -41,6 +41,15 @@ mca_coll_base_module_t *mca_coll_acoll_comm_query(struct ompi_communicator_t *co
         return NULL;
     }
 
+    if (OMPI_COMM_IS_INTER(comm)) {
+        *priority = 0;
+        return NULL;
+    }
+    if (OMPI_COMM_IS_INTRA(comm) && ompi_comm_size(comm) < 2) {
+        *priority = 0;
+        return NULL;
+    }
+
     *priority = mca_coll_acoll_priority;
 
     /* Set topology params */
diff --git a/ompi/mca/coll/acoll/coll_acoll_reduce.c b/ompi/mca/coll/acoll/coll_acoll_reduce.c
index 08afa893ee7..82082bb9681 100644
--- a/ompi/mca/coll/acoll/coll_acoll_reduce.c
+++ b/ompi/mca/coll/acoll/coll_acoll_reduce.c
@@ -382,11 +382,11 @@ int mca_coll_acoll_reduce_intra(const void *sbuf, void *rbuf, int count,
                                                    module);
             } else {
                 return ompi_coll_base_reduce_intra_binomial(sbuf, rbuf, count, dtype, op,
-                                                            root, comm, module, 0, 0);
+                                                                   root, comm, module, 0, 0);
             }
 #else
             return ompi_coll_base_reduce_intra_binomial(sbuf, rbuf, count, dtype, op, root,
-                                                        comm, module, 0, 0);
+                                                               comm, module, 0, 0);
 #endif
         }
     } else {
diff --git a/ompi/mca/coll/acoll/coll_acoll_utils.h b/ompi/mca/coll/acoll/coll_acoll_utils.h
index a5223a77f91..5832c067ac5 100644
--- a/ompi/mca/coll/acoll/coll_acoll_utils.h
+++ b/ompi/mca/coll/acoll/coll_acoll_utils.h
@@ -262,6 +262,9 @@ static inline int mca_coll_acoll_comm_split_init(ompi_communicator_t *comm,
     mca_coll_base_module_allreduce_fn_t coll_allreduce_org = (comm)->c_coll->coll_allreduce;
     mca_coll_base_module_allgather_fn_t coll_allgather_org = (comm)->c_coll->coll_allgather;
     mca_coll_base_module_bcast_fn_t coll_bcast_org = (comm)->c_coll->coll_bcast;
+    mca_coll_base_module_allreduce_fn_t coll_allreduce_loc, coll_allreduce_soc;
+    mca_coll_base_module_allgather_fn_t coll_allgather_loc, coll_allgather_soc;
+    mca_coll_base_module_bcast_fn_t coll_bcast_loc, coll_bcast_soc;
     coll_acoll_subcomms_t *subc;
     int err;
     int size = ompi_comm_size(comm);
@@ -362,6 +365,21 @@ static inline int mca_coll_acoll_comm_split_init(ompi_communicator_t *comm,
             subc->base_root[MCA_COLL_ACOLL_L3CACHE][i] = -1;
             subc->base_root[MCA_COLL_ACOLL_NUMA][i] = -1;
         }
+        /* Store original collectives for local and socket comms */
+        coll_allreduce_loc = (subc->local_comm)->c_coll->coll_allreduce;
+        coll_allgather_loc = (subc->local_comm)->c_coll->coll_allgather;
+        coll_bcast_loc = (subc->local_comm)->c_coll->coll_bcast;
+        (subc->local_comm)->c_coll->coll_allgather = ompi_coll_base_allgather_intra_ring;
+        (subc->local_comm)->c_coll->coll_allreduce
+            = ompi_coll_base_allreduce_intra_recursivedoubling;
+        (subc->local_comm)->c_coll->coll_bcast = ompi_coll_base_bcast_intra_basic_linear;
+        coll_allreduce_soc = (subc->socket_comm)->c_coll->coll_allreduce;
+        coll_allgather_soc = (subc->socket_comm)->c_coll->coll_allgather;
+        coll_bcast_soc = (subc->socket_comm)->c_coll->coll_bcast;
+        (subc->socket_comm)->c_coll->coll_allgather = ompi_coll_base_allgather_intra_ring;
+        (subc->socket_comm)->c_coll->coll_allreduce
+            = ompi_coll_base_allreduce_intra_recursivedoubling;
+        (subc->socket_comm)->c_coll->coll_bcast = ompi_coll_base_bcast_intra_basic_linear;
     }
 
     /* Further subcommunicators based on root */
@@ -519,6 +537,14 @@ static inline int mca_coll_acoll_comm_split_init(ompi_communicator_t *comm,
         }
     }
 
+    /* Restore originals for local and socket comms */
+    (subc->local_comm)->c_coll->coll_allreduce = coll_allreduce_loc;
+    (subc->local_comm)->c_coll->coll_allgather = coll_allgather_loc;
+    (subc->local_comm)->c_coll->coll_bcast = coll_bcast_loc;
+    (subc->socket_comm)->c_coll->coll_allreduce = coll_allreduce_soc;
+    (subc->socket_comm)->c_coll->coll_allgather = coll_allgather_soc;
+    (subc->socket_comm)->c_coll->coll_bcast = coll_bcast_soc;
+
     /* For collectives where order is important (like gather, allgather),
      * split based on ranks. This is optimal for global communicators with
      * equal split among nodes, but suboptimal for other cases.
@@ -590,6 +616,7 @@ static inline int coll_acoll_init(mca_coll_base_module_t *module, ompi_communica
     data = (coll_acoll_data_t *) malloc(sizeof(coll_acoll_data_t));
     if (NULL == data) {
         line = __LINE__;
+        ret = OMPI_ERR_OUT_OF_RESOURCE;
         goto error_hndl;
     }
     size = ompi_comm_size(comm);
@@ -601,6 +628,7 @@ static inline int coll_acoll_init(mca_coll_base_module_t *module, ompi_communica
         data->scratch = (char *) malloc(subc->xpmem_buf_size);
         if (NULL == data->scratch) {
             line = __LINE__;
+            ret = OMPI_ERR_OUT_OF_RESOURCE;
             goto error_hndl;
         }
     } else {
@@ -611,41 +639,49 @@ static inline int coll_acoll_init(mca_coll_base_module_t *module, ompi_communica
     data->allseg_id = (xpmem_segid_t *) malloc(sizeof(xpmem_segid_t) * size);
     if (NULL == data->allseg_id) {
         line = __LINE__;
+        ret = OMPI_ERR_OUT_OF_RESOURCE;
         goto error_hndl;
     }
     data->all_apid = (xpmem_apid_t *) malloc(sizeof(xpmem_apid_t) * size);
     if (NULL == data->all_apid) {
         line = __LINE__;
+        ret = OMPI_ERR_OUT_OF_RESOURCE;
         goto error_hndl;
     }
     data->allshm_sbuf = (void **) malloc(sizeof(void *) * size);
     if (NULL == data->allshm_sbuf) {
         line = __LINE__;
+        ret = OMPI_ERR_OUT_OF_RESOURCE;
         goto error_hndl;
     }
     data->allshm_rbuf = (void **) malloc(sizeof(void *) * size);
     if (NULL == data->allshm_rbuf) {
         line = __LINE__;
+        ret = OMPI_ERR_OUT_OF_RESOURCE;
         goto error_hndl;
     }
     data->xpmem_saddr = (void **) malloc(sizeof(void *) * size);
     if (NULL == data->xpmem_saddr) {
         line = __LINE__;
+        ret = OMPI_ERR_OUT_OF_RESOURCE;
         goto error_hndl;
     }
     data->xpmem_raddr = (void **) malloc(sizeof(void *) * size);
     if (NULL == data->xpmem_raddr) {
         line = __LINE__;
+        ret = OMPI_ERR_OUT_OF_RESOURCE;
         goto error_hndl;
     }
     data->rcache = (mca_rcache_base_module_t **) malloc(sizeof(mca_rcache_base_module_t *) * size);
     if (NULL == data->rcache) {
         line = __LINE__;
+        ret = OMPI_ERR_OUT_OF_RESOURCE;
         goto error_hndl;
     }
     seg_id = xpmem_make(0, XPMEM_MAXADDR_SIZE, XPMEM_PERMIT_MODE, (void *) 0666);
     if (seg_id == -1) {
         line = __LINE__;
+        ret = -1;
         goto error_hndl;
     }