diff --git a/src/core/ddsc/include/dds/ddsc/dds_public_qos.h b/src/core/ddsc/include/dds/ddsc/dds_public_qos.h
index 95fa4fe..b8fc7fa 100644
--- a/src/core/ddsc/include/dds/ddsc/dds_public_qos.h
+++ b/src/core/ddsc/include/dds/ddsc/dds_public_qos.h
@@ -501,7 +501,7 @@ DDS_EXPORT void dds_qset_ignorelocal (
  * @brief Get the userdata from a qos structure
  *
  * @param[in] qos - Pointer to a dds_qos_t structure storing the policy
- * @param[in,out] value - Pointer that will store the userdata
+ * @param[in,out] value - Pointer that will store the userdata.  If sz = 0, then a null pointer, else it is a pointer to an allocated buffer of sz+1 bytes where the last byte is always 0
  * @param[in,out] sz - Pointer that will store the size of userdata
  *
  * @returns - false iff any of the arguments is invalid or the qos is not present in the qos object
@@ -512,7 +512,7 @@ DDS_EXPORT bool dds_qget_userdata (const dds_qos_t * __restrict qos, void **valu
  * @brief Get the topicdata from a qos structure
  *
  * @param[in] qos - Pointer to a dds_qos_t structure storing the policy
- * @param[in,out] value - Pointer that will store the topicdata
+ * @param[in,out] value - Pointer that will store the topicdata.  If sz = 0, then a null pointer, else it is a pointer to an allocated buffer of sz+1 bytes where the last byte is always 0
  * @param[in,out] sz - Pointer that will store the size of topicdata
  *
  * @returns - false iff any of the arguments is invalid or the qos is not present in the qos object
@@ -523,7 +523,7 @@ DDS_EXPORT bool dds_qget_topicdata (const dds_qos_t * __restrict qos, void **val
  * @brief Get the groupdata from a qos structure
  *
  * @param[in] qos - Pointer to a dds_qos_t structure storing the policy
- * @param[in,out] value - Pointer that will store the groupdata
+ * @param[in,out] value - Pointer that will store the groupdata.  If sz = 0, then a null pointer, else it is a pointer to an allocated buffer of sz+1 bytes where the last byte is always 0
  * @param[in,out] sz - Pointer that will store the size of groupdata
  *
  * @returns - false iff any of the arguments is invalid or the qos is not present in the qos object
diff --git a/src/core/ddsc/src/dds_qos.c b/src/core/ddsc/src/dds_qos.c
index 02988bf..d95add8 100644
--- a/src/core/ddsc/src/dds_qos.c
+++ b/src/core/ddsc/src/dds_qos.c
@@ -43,6 +43,7 @@ dds_qos_data_copy_out(
     void ** value,
     size_t * sz)
 {
+    assert (data->length < UINT32_MAX);
     if (sz == NULL && value != NULL) {
         return false;
     }
@@ -51,9 +52,10 @@ dds_qos_data_copy_out(
     }
     if (value) {
         if (data->length != 0) {
-            assert(data->value);
-            *value = dds_alloc(data->length);
-            memcpy(*value, data->value, data->length);
+            assert (data->value);
+            *value = dds_alloc (data->length + 1);
+            memcpy (*value, data->value, data->length);
+            ((char *) (*value))[data->length] = 0;
         } else {
             *value = NULL;
         }
@@ -66,7 +68,7 @@ validate_octetseq(
     const nn_octetseq_t* seq)
 {
     /* default value is NULL with length 0 */
-    return (((seq->length == 0) && (seq->value == NULL)) || (seq->length > 0));
+    return (((seq->length == 0) && (seq->value == NULL)) || (seq->length > 0 && seq->length < UINT32_MAX));
 }
 
 bool
diff --git a/src/core/ddsi/src/q_plist.c b/src/core/ddsi/src/q_plist.c
index fed7f43..d44cec1 100644
--- a/src/core/ddsi/src/q_plist.c
+++ b/src/core/ddsi/src/q_plist.c
@@ -144,7 +144,7 @@ static int validate_octetseq (const struct dd *dd, size_t *len)
   if (dd->bufsz < offsetof (struct cdroctetseq, value))
     return Q_ERR_INVALID;
   *len = dd->bswap ? bswap4u (x->len) : x->len;
-  if (*len > dd->bufsz - offsetof (struct cdroctetseq, value))
+  if (*len > dd->bufsz - offsetof (struct cdroctetseq, value) || *len >= UINT32_MAX)
     return Q_ERR_INVALID;
   return 0;
 }
@@ -158,7 +158,7 @@ static int alias_octetseq (nn_octetseq_t *oseq, const struct dd *dd)
   else
   {
     const struct cdroctetseq *x = (const struct cdroctetseq *) dd->buf;
-    assert(len <= UINT32_MAX); /* it really is an uint32_t on the wire */
+    assert(len < UINT32_MAX); /* it really is an uint32_t on the wire */
     oseq->length = (uint32_t)len;
     oseq->value = (len == 0) ? NULL : (unsigned char *) x->value;
     return 0;
@@ -167,7 +167,7 @@ static int alias_octetseq (nn_octetseq_t *oseq, const struct dd *dd)
 
 static int alias_blob (nn_octetseq_t *oseq, const struct dd *dd)
 {
-  assert (dd->bufsz <= UINT32_MAX);
+  assert (dd->bufsz < UINT32_MAX);
   oseq->length = (uint32_t)dd->bufsz;
   oseq->value = (oseq->length == 0) ? NULL : (unsigned char *) dd->buf;
   return 0;