diff --git a/src/core/ddsc/src/dds_stream.c b/src/core/ddsc/src/dds_stream.c
index 2c724a9..fc706d5 100644
--- a/src/core/ddsc/src/dds_stream.c
+++ b/src/core/ddsc/src/dds_stream.c
@@ -77,23 +77,27 @@ static void dds_cdr_alignto (dds_istream_t * __restrict s, uint32_t a)
   assert (s->m_index < s->m_size);
 }
 
-static void dds_cdr_alignto_clear_and_resize (dds_ostream_t * __restrict s, uint32_t a, uint32_t extra)
+static uint32_t dds_cdr_alignto_clear_and_resize (dds_ostream_t * __restrict s, uint32_t a, uint32_t extra)
 {
   const uint32_t m = s->m_index % a;
   if (m == 0)
+  {
     dds_cdr_resize (s, extra);
+    return 0;
+  }
   else
   {
-    uint32_t pad = a - m;
+    const uint32_t pad = a - m;
     dds_cdr_resize (s, pad + extra);
-    while (pad--)
+    for (uint32_t i = 0; i < pad; i++)
       s->m_buffer[s->m_index++] = 0;
+    return pad;
   }
 }
 
-static void dds_cdr_alignto_clear_and_resize_be (dds_ostreamBE_t * __restrict s, uint32_t a, uint32_t extra)
+static uint32_t dds_cdr_alignto_clear_and_resize_be (dds_ostreamBE_t * __restrict s, uint32_t a, uint32_t extra)
 {
-  dds_cdr_alignto_clear_and_resize (&s->x, a, extra);
+  return dds_cdr_alignto_clear_and_resize (&s->x, a, extra);
 }
 
 static uint8_t dds_is_get1 (dds_istream_t * __restrict s)
@@ -1644,13 +1648,15 @@ void dds_ostream_add_to_serdata_default (dds_ostream_t * __restrict s, struct dd
 {
   /* DDSI requires 4 byte alignment */
 
-  dds_cdr_alignto_clear_and_resize (s, 4, 0);
+  const uint32_t pad = dds_cdr_alignto_clear_and_resize (s, 4, 0);
+  assert (pad <= 3);
 
   /* Reset data pointer as stream may have reallocated */
 
   (*d) = (void *) s->m_buffer;
   (*d)->pos = (s->m_index - (uint32_t) offsetof (struct ddsi_serdata_default, data));
   (*d)->size = (s->m_size - (uint32_t) offsetof (struct ddsi_serdata_default, data));
+  (*d)->hdr.options = toBE2u ((uint16_t) pad);
 }
 
 void dds_ostreamBE_from_serdata_default (dds_ostreamBE_t * __restrict s, struct ddsi_serdata_default * __restrict d)
@@ -1665,11 +1671,13 @@ void dds_ostreamBE_add_to_serdata_default (dds_ostreamBE_t * __restrict s, struc
 {
   /* DDSI requires 4 byte alignment */
 
-  dds_cdr_alignto_clear_and_resize_be (s, 4, 0);
+  const uint32_t pad = dds_cdr_alignto_clear_and_resize_be (s, 4, 0);
+  assert (pad <= 3);
 
   /* Reset data pointer as stream may have reallocated */
 
   (*d) = (void *) s->x.m_buffer;
   (*d)->pos = (s->x.m_index - (uint32_t) offsetof (struct ddsi_serdata_default, data));
   (*d)->size = (s->x.m_size - (uint32_t) offsetof (struct ddsi_serdata_default, data));
+  (*d)->hdr.options = toBE2u ((uint16_t) pad);
 }
diff --git a/src/core/ddsi/src/ddsi_serdata_default.c b/src/core/ddsi/src/ddsi_serdata_default.c
index 65ab5d4..630c6c0 100644
--- a/src/core/ddsi/src/ddsi_serdata_default.c
+++ b/src/core/ddsi/src/ddsi_serdata_default.c
@@ -301,7 +301,13 @@ static struct ddsi_serdata_default *serdata_default_from_ser_common (const struc
 
   const bool needs_bswap = (d->hdr.identifier != NATIVE_ENCODING);
   d->hdr.identifier = NATIVE_ENCODING;
-  if (!dds_stream_normalize (d->data, d->pos, needs_bswap, tp, kind == SDK_KEY))
+  const uint32_t pad = fromBE2u (d->hdr.options) & 2;
+  if (d->pos < pad)
+  {
+    ddsi_serdata_unref (&d->c);
+    return NULL;
+  }
+  else if (!dds_stream_normalize (d->data, d->pos - pad, needs_bswap, tp, kind == SDK_KEY))
   {
     ddsi_serdata_unref (&d->c);
     return NULL;