diff --git a/config/ompi_check_ucx.m4 b/config/ompi_check_ucx.m4
index dc5a8181825..6901a46127e 100644
--- a/config/ompi_check_ucx.m4
+++ b/config/ompi_check_ucx.m4
@@ -104,44 +104,58 @@ AC_DEFUN([OMPI_CHECK_UCX],[
                   old_CPPFLAGS="$CPPFLAGS"
                   AS_IF([test -n "$ompi_check_ucx_dir"],
                         [CPPFLAGS="$CPPFLAGS -I$ompi_check_ucx_dir/include"])
-                  AC_CHECK_DECLS([ucp_tag_send_nbr],
-                                 [AC_DEFINE([HAVE_UCP_TAG_SEND_NBR],[1],
-                                            [have ucp_tag_send_nbr()])], [],
-                                 [#include <ucp/api/ucp.h>])
-                  AC_CHECK_DECLS([ucp_ep_flush_nb, ucp_worker_flush_nb,
-                                  ucp_request_check_status, ucp_put_nb, ucp_get_nb,
-                                  ucp_put_nbx, ucp_get_nbx, ucp_atomic_op_nbx],
-                                 [], [],
-                                 [#include <ucp/api/ucp.h>])
-                  AC_CHECK_DECLS([ucm_test_events,
-                                  ucm_test_external_events],
-                                 [], [],
-                                 [#include <ucm/api/ucm.h>])
-                  AC_CHECK_DECLS([UCP_ATOMIC_POST_OP_AND,
-                                  UCP_ATOMIC_POST_OP_OR,
-                                  UCP_ATOMIC_POST_OP_XOR,
-                                  UCP_ATOMIC_FETCH_OP_FAND,
-                                  UCP_ATOMIC_FETCH_OP_FOR,
-                                  UCP_ATOMIC_FETCH_OP_FXOR,
-                                  UCP_PARAM_FIELD_ESTIMATED_NUM_PPN],
-                                 [], [],
-                                 [#include <ucp/api/ucp.h>])
-                  AC_CHECK_DECLS([UCP_WORKER_ATTR_FIELD_ADDRESS_FLAGS],
-                                 [AC_DEFINE([HAVE_UCP_WORKER_ADDRESS_FLAGS], [1],
-                                            [have worker address attribute])], [],
-                                 [#include <ucp/api/ucp.h>])
-                  AC_CHECK_DECLS([UCP_ATTR_FIELD_MEMORY_TYPES],
-                                 [AC_DEFINE([HAVE_UCP_ATTR_MEMORY_TYPES], [1],
-                                            [have memory types attribute])], [],
-                                 [#include <ucp/api/ucp.h>])
-                  AC_CHECK_DECLS([ucp_tag_send_nbx,
-                                  ucp_tag_send_sync_nbx,
-                                  ucp_tag_recv_nbx],
-                                 [], [],
-                                 [#include <ucp/api/ucp.h>])
-                  AC_CHECK_TYPES([ucp_request_param_t],
-                                 [], [],
-                                 [[#include <ucp/api/ucp.h>]])
+                  # Turn off UCX version v1.8 due to issue #8321
+                  AC_MSG_CHECKING([UCX version])
+                  AC_PREPROC_IFELSE([AC_LANG_PROGRAM([#include <ucp/api/ucp_version.h>
+                                                      #if (UCP_API_MAJOR == 1) && (UCP_API_MINOR == 8)
+                                                      #error "Invalid version"
+                                                      #endif], [])],
+                                    [AC_MSG_RESULT([ok (not 1.8.x)])],
+                                    [AC_MSG_RESULT([bad (1.8.x)])
+                                     AC_MSG_WARN([UCX support skipped because version 1.8.x was found, which has a known catastrophic issue.])
+                                     AC_MSG_WARN([Please upgrade to UCX version 1.9 or higher.])
+                                     ompi_check_ucx_happy=no])
+                  AS_IF([test "$ompi_check_ucx_happy" = yes],
+                        [
+                         AC_CHECK_DECLS([ucp_tag_send_nbr],
+                                        [AC_DEFINE([HAVE_UCP_TAG_SEND_NBR],[1],
+                                                   [have ucp_tag_send_nbr()])], [],
+                                        [#include <ucp/api/ucp.h>])
+                         AC_CHECK_DECLS([ucp_ep_flush_nb, ucp_worker_flush_nb,
+                                         ucp_request_check_status, ucp_put_nb, ucp_get_nb,
+                                         ucp_put_nbx, ucp_get_nbx, ucp_atomic_op_nbx],
+                                        [], [],
+                                        [#include <ucp/api/ucp.h>])
+                         AC_CHECK_DECLS([ucm_test_events,
+                                         ucm_test_external_events],
+                                        [], [],
+                                        [#include <ucm/api/ucm.h>])
+                         AC_CHECK_DECLS([UCP_ATOMIC_POST_OP_AND,
+                                         UCP_ATOMIC_POST_OP_OR,
+                                         UCP_ATOMIC_POST_OP_XOR,
+                                         UCP_ATOMIC_FETCH_OP_FAND,
+                                         UCP_ATOMIC_FETCH_OP_FOR,
+                                         UCP_ATOMIC_FETCH_OP_FXOR,
+                                         UCP_PARAM_FIELD_ESTIMATED_NUM_PPN],
+                                        [], [],
+                                        [#include <ucp/api/ucp.h>])
+                         AC_CHECK_DECLS([UCP_WORKER_ATTR_FIELD_ADDRESS_FLAGS],
+                                        [AC_DEFINE([HAVE_UCP_WORKER_ADDRESS_FLAGS], [1],
+                                                   [have worker address attribute])], [],
+                                        [#include <ucp/api/ucp.h>])
+                         AC_CHECK_DECLS([UCP_ATTR_FIELD_MEMORY_TYPES],
+                                        [AC_DEFINE([HAVE_UCP_ATTR_MEMORY_TYPES], [1],
+                                                   [have memory types attribute])], [],
+                                        [#include <ucp/api/ucp.h>])
+                         AC_CHECK_DECLS([ucp_tag_send_nbx,
+                                         ucp_tag_send_sync_nbx,
+                                         ucp_tag_recv_nbx],
+                                        [], [],
+                                        [#include <ucp/api/ucp.h>])
+                         AC_CHECK_TYPES([ucp_request_param_t],
+                                        [], [],
+                                        [[#include <ucp/api/ucp.h>]])
+                        ])
                   CPPFLAGS=$old_CPPFLAGS
 
                   OPAL_SUMMARY_ADD([[Transports]],[[Open UCX]],[$1],[$ompi_check_ucx_happy])])])
diff --git a/ompi/mca/pml/ucx/pml_ucx.c b/ompi/mca/pml/ucx/pml_ucx.c
index 6be18579d99..fc46995d940 100644
--- a/ompi/mca/pml/ucx/pml_ucx.c
+++ b/ompi/mca/pml/ucx/pml_ucx.c
@@ -186,12 +186,23 @@ static int mca_pml_ucx_recv_worker_address(ompi_proc_t *proc,
 
 int mca_pml_ucx_open(void)
 {
+    unsigned major_version, minor_version, release_number;
     ucp_context_attr_t attr;
     ucp_params_t params;
     ucp_config_t *config;
     ucs_status_t status;
 
-    PML_UCX_VERBOSE(1, "mca_pml_ucx_open");
+    /* Check version */
+    ucp_get_version(&major_version, &minor_version, &release_number);
+    PML_UCX_VERBOSE(1, "mca_pml_ucx_open: UCX version %u.%u.%u",
+                    major_version, minor_version, release_number);
+
+    if ((major_version == 1) && (minor_version == 8)) {
+        /* disabled due to issue #8321 */
+        PML_UCX_VERBOSE(1, "UCX PML is disabled because the run-time UCX version "
+                           "is 1.8, which has a known catastrophic issue");
+        return OMPI_ERROR;
+    }
 
     /* Read options */
     status = ucp_config_read("MPI", NULL, &config);
@@ -694,7 +705,7 @@ int mca_pml_ucx_isend_init(const void *buf, size_t count, ompi_datatype_t *datat
 }
 
 static ucs_status_ptr_t
-mca_pml_ucx_bsend(ucp_ep_h ep, const void *buf, size_t count, 
+mca_pml_ucx_bsend(ucp_ep_h ep, const void *buf, size_t count,
                   ompi_datatype_t *datatype, uint64_t pml_tag)
 {
     ompi_request_t *req;
@@ -717,7 +728,7 @@ mca_pml_ucx_bsend(ucp_ep_h ep, const void *buf, size_t count,
         PML_UCX_ERROR("bsend: failed to allocate buffer");
         return UCS_STATUS_PTR(OMPI_ERROR);
     }
-    
+
     iov_count    = 1;
     iov.iov_base = packed_data;
     iov.iov_len  = packed_length;
@@ -805,8 +816,8 @@ int mca_pml_ucx_isend(const void *buf, size_t count, ompi_datatype_t *datatype,
     ompi_request_t *req;
     ucp_ep_h ep;
 
-    PML_UCX_TRACE_SEND("i%ssend request *%p", 
-                       buf, count, datatype, dst, tag, mode, comm, 
+    PML_UCX_TRACE_SEND("i%ssend request *%p",
+                       buf, count, datatype, dst, tag, mode, comm,
                        mode == MCA_PML_BASE_SEND_BUFFERED ? "b" : "",
                        (void*)request)