diff --git a/ompi/mca/pml/ob1/pml_ob1_comm.h b/ompi/mca/pml/ob1/pml_ob1_comm.h
index 8a99b1cf70..7fac7aa628 100644
--- a/ompi/mca/pml/ob1/pml_ob1_comm.h
+++ b/ompi/mca/pml/ob1/pml_ob1_comm.h
@@ -31,7 +31,7 @@ extern "C" {
 struct mca_pml_ob1_comm_proc_t {
     opal_object_t super;
     uint16_t expected_sequence;    /**< send message sequence number - receiver side */
-    volatile uint32_t send_sequence; /**< send side sequence number */
+    volatile int32_t send_sequence; /**< send side sequence number */
     opal_list_t frags_cant_match;  /**< out-of-order fragment queues */
     opal_list_t specific_receives; /**< queues of unmatched specific receives */
     opal_list_t unexpected_frags;  /**< unexpected fragment queues */
diff --git a/ompi/mca/pml/ob1/pml_ob1_recvreq.h b/ompi/mca/pml/ob1/pml_ob1_recvreq.h
index c33402d785..ae6fa406e3 100644
--- a/ompi/mca/pml/ob1/pml_ob1_recvreq.h
+++ b/ompi/mca/pml/ob1/pml_ob1_recvreq.h
@@ -35,7 +35,7 @@ struct  mca_pml_ob1_recv_request_t {
     struct mca_mpool_base_chunk_t* req_chunk;
     struct mca_mpool_base_reg_mpool_t* req_mpool;
     ompi_ptr_t req_send;
-    int32_t req_lock;
+    volatile int32_t req_lock;
     size_t  req_pipeline_depth;
     size_t  req_bytes_received;
     size_t  req_bytes_delivered;
diff --git a/ompi/mca/pml/ob1/pml_ob1_sendreq.h b/ompi/mca/pml/ob1/pml_ob1_sendreq.h
index 593986ac2a..1ce74852d7 100644
--- a/ompi/mca/pml/ob1/pml_ob1_sendreq.h
+++ b/ompi/mca/pml/ob1/pml_ob1_sendreq.h
@@ -40,7 +40,7 @@ struct mca_pml_ob1_send_request_t {
     volatile int32_t req_state;
     struct mca_mpool_base_chunk_t* req_chunk;
     ompi_ptr_t req_recv;
-    int32_t req_lock;
+    volatile int32_t req_lock;
     size_t req_pipeline_depth;
     size_t req_bytes_delivered;
     size_t req_send_offset;