diff --git a/Testing/unit/hg/mercury_rpc_cb.c b/Testing/unit/hg/mercury_rpc_cb.c
index 277e2226..ba4538d1 100644
--- a/Testing/unit/hg/mercury_rpc_cb.c
+++ b/Testing/unit/hg/mercury_rpc_cb.c
@@ -186,8 +186,16 @@ HG_TEST_RPC_CB(hg_test_rpc_open, handle)
     struct hg_unit_info *info = (struct hg_unit_info *) HG_Class_get_data(
         HG_Get_info(handle)->hg_class);
     hg_size_t payload_size = HG_Get_input_payload_size(handle);
+#ifdef HG_HAS_XDR
+    size_t expected_string_payload_size =     /* note xdr rounding rules */
+        sizeof(uint64_t) +                    /* length */
+        RNDUP(strlen(HG_TEST_RPC_PATH) + 1) + /* string data, inc \0 at end */
+        RNDUP(sizeof(uint8_t)) +              /* is_const */
+        RNDUP(sizeof(uint8_t));               /* is_owned */
+#else
     size_t expected_string_payload_size =
         strlen(HG_TEST_RPC_PATH) + sizeof(uint64_t) + 3;
+#endif
 
     HG_TEST_CHECK_ERROR(
         payload_size != sizeof(rpc_handle_t) + expected_string_payload_size,
diff --git a/Testing/unit/hg/test_rpc.c b/Testing/unit/hg/test_rpc.c
index 63e25607..49a52a87 100644
--- a/Testing/unit/hg/test_rpc.c
+++ b/Testing/unit/hg/test_rpc.c
@@ -176,8 +176,16 @@ hg_test_rpc_input(hg_handle_t handle, hg_addr_t addr, hg_id_t rpc_id,
     rpc_open_in_t in_struct = {
         .handle = rpc_open_handle, .path = HG_TEST_RPC_PATH};
     hg_size_t payload_size;
+#ifdef HG_HAS_XDR
+    size_t expected_string_payload_size =     /* note xdr rounding rules */
+        sizeof(uint64_t) +                    /* length */
+        RNDUP(strlen(HG_TEST_RPC_PATH) + 1) + /* string data, inc \0 at end */
+        RNDUP(sizeof(uint8_t)) +              /* is_const */
+        RNDUP(sizeof(uint8_t));               /* is_owned */
+#else
     size_t expected_string_payload_size =
         strlen(HG_TEST_RPC_PATH) + sizeof(uint64_t) + 3;
+#endif
     unsigned int flag;
     int rc;
 
diff --git a/src/mercury.c b/src/mercury.c
index 0bcddd83..903e7e9f 100644
--- a/src/mercury.c
+++ b/src/mercury.c
@@ -781,13 +781,8 @@ hg_set_struct(struct hg_private_handle *hg_handle,
     ret = hg_header_proc(HG_ENCODE, buf, buf_size, hg_header);
     HG_CHECK_SUBSYS_HG_ERROR(rpc, error, ret, "Could not process header");
 
-#ifdef HG_HAS_XDR
-    /* XDR requires entire buffer payload */
-    *payload_size = buf_size;
-#else
     /* Only send the actual size of the data, not the entire buffer */
     *payload_size = hg_proc_get_size_used(proc) + header_offset;
-#endif
 
     return HG_SUCCESS;
 
diff --git a/src/mercury_proc.h b/src/mercury_proc.h
index 8f1db2e6..c62e806c 100644
--- a/src/mercury_proc.h
+++ b/src/mercury_proc.h
@@ -110,14 +110,14 @@ typedef enum { HG_CRC16, HG_CRC32, HG_CRC64, HG_NOHASH } hg_proc_hash_t;
 #ifdef HG_HAS_XDR
 #    define HG_PROC_TYPE(proc, type, data, label, ret)                         \
         do {                                                                   \
-            HG_PROC_CHECK_SIZE(proc, sizeof(type), label, ret);                \
+            HG_PROC_CHECK_SIZE(proc, RNDUP(sizeof(type)), label, ret);         \
                                                                                \
             if (xdr_##type(hg_proc_get_xdr_ptr(proc), data) == 0) {            \
                 ret = HG_PROTOCOL_ERROR;                                       \
                 goto label;                                                    \
             }                                                                  \
                                                                                \
-            HG_PROC_UPDATE(proc, sizeof(type));                                \
+            HG_PROC_UPDATE(proc, RNDUP(sizeof(type)));                         \
             HG_PROC_CHECKSUM_UPDATE(proc, data, sizeof(type));                 \
         } while (0)
 #else
@@ -147,15 +147,15 @@ typedef enum { HG_CRC16, HG_CRC32, HG_CRC64, HG_NOHASH } hg_proc_hash_t;
 #ifdef HG_HAS_XDR
 #    define HG_PROC_BYTES(proc, data, size, label, ret)                        \
         do {                                                                   \
-            HG_PROC_CHECK_SIZE(proc, size, label, ret);                        \
+            HG_PROC_CHECK_SIZE(proc, RNDUP(size), label, ret);                 \
                                                                                \
-            if (xdr_bytes(hg_proc_get_xdr_ptr(proc), (char **) &data,          \
-                    (u_int *) &size, UINT_MAX) == 0) {                         \
+            if (xdr_opaque(hg_proc_get_xdr_ptr(proc), (char *) data, size) ==  \
+                0) {                                                           \
                 ret = HG_PROTOCOL_ERROR;                                       \
                 goto label;                                                    \
             }                                                                  \
                                                                                \
-            HG_PROC_UPDATE(proc, size);                                        \
+            HG_PROC_UPDATE(proc, RNDUP(size));                                 \
             HG_PROC_CHECKSUM_UPDATE(proc, data, size);                         \
         } while (0)
 #else