diff --git a/src/core/ddsi/src/ddsi_serdata_default.c b/src/core/ddsi/src/ddsi_serdata_default.c
index 630c6c0..8c5b38c 100644
--- a/src/core/ddsi/src/ddsi_serdata_default.c
+++ b/src/core/ddsi/src/ddsi_serdata_default.c
@@ -102,17 +102,13 @@ static void *serdata_default_append (struct ddsi_serdata_default **d, size_t n)
 
 static void *serdata_default_append_aligned (struct ddsi_serdata_default **d, size_t n, size_t a)
 {
-#if CLEAR_PADDING
-  size_t pos0 = st->pos;
-#endif
+  size_t pos0 = (*d)->pos;
   char *p;
   assert (ispowerof2_size (a));
   (*d)->pos = (uint32_t) alignup_size ((*d)->pos, a);
   p = serdata_default_append (d, n);
-#if CLEAR_PADDING
-  if (p && (*d)->pos > pos0)
-    memset ((*d)->data + pos0, 0, (*d)->pos - pos0);
-#endif
+  while (pos0 < (*d)->pos)
+    (*d)->data[pos0++] = 0;
   return p;
 }
 
@@ -512,6 +508,7 @@ static struct ddsi_serdata *serdata_default_from_sample_rawcdr (const struct dds
     return NULL;
   assert (sample->keysize <= 16);
   serdata_default_append_blob (&d, 1, sample->size, sample->blob);
+  serdata_default_append_aligned (&d, 0, 4);
   d->keyhash.m_set = 1;
   d->keyhash.m_iskey = 1;
   if (sample->keysize == 0)
diff --git a/src/core/ddsi/src/q_ddsi_discovery.c b/src/core/ddsi/src/q_ddsi_discovery.c
index 3973840..9218611 100644
--- a/src/core/ddsi/src/q_ddsi_discovery.c
+++ b/src/core/ddsi/src/q_ddsi_discovery.c
@@ -289,6 +289,7 @@ int spdp_write (struct participant *pp)
   /* Add PrismTech specific version information */
   {
     ps.present |= PP_PRISMTECH_PARTICIPANT_VERSION_INFO;
+    memset (&ps.prismtech_participant_version_info, 0, sizeof (ps.prismtech_participant_version_info));
     ps.prismtech_participant_version_info.version = 0;
     ps.prismtech_participant_version_info.flags =
       NN_PRISMTECH_FL_DDSI2_PARTICIPANT_FLAG |
diff --git a/src/core/ddsi/src/q_plist.c b/src/core/ddsi/src/q_plist.c
index 7d396c3..0cf2da1 100644
--- a/src/core/ddsi/src/q_plist.c
+++ b/src/core/ddsi/src/q_plist.c
@@ -158,8 +158,13 @@ static const void *deser_generic_src (const void * __restrict src, size_t *srcof
 
 static void *ser_generic_align4 (char * __restrict p, size_t * __restrict off)
 {
-  *off = align4size (*off);
-  return p + *off;
+  const size_t off1 = align4size (*off);
+  size_t pad = off1 - *off;
+  char *dst = p + *off;
+  *off = off1;
+  while (pad--)
+    *dst++ = 0;
+  return dst;
 }
 
 static dds_return_t deser_uint32 (uint32_t *dst, const struct dd * __restrict dd, size_t * __restrict off)
diff --git a/src/core/ddsi/src/q_xmsg.c b/src/core/ddsi/src/q_xmsg.c
index 8f942b0..f21214d 100644
--- a/src/core/ddsi/src/q_xmsg.c
+++ b/src/core/ddsi/src/q_xmsg.c
@@ -506,7 +506,7 @@ void *nn_xmsg_submsg_from_marker (struct nn_xmsg *msg, struct nn_xmsg_marker mar
   return msg->data->payload + marker.offset;
 }
 
-void * nn_xmsg_append (struct nn_xmsg *m, struct nn_xmsg_marker *marker, size_t sz)
+void *nn_xmsg_append (struct nn_xmsg *m, struct nn_xmsg_marker *marker, size_t sz)
 {
   static const size_t a = 4;
 
@@ -809,13 +809,10 @@ void *nn_xmsg_addpar (struct nn_xmsg *m, nn_parameterid_t pid, size_t len)
   phdr->parameterid = pid;
   phdr->length = (uint16_t) len4;
   p = (char *) (phdr + 1);
-  if (len4 > len)
-  {
-    /* zero out padding bytes added to satisfy parameter alignment --
-       alternative: zero out, but this way valgrind/purify can tell us
-       where we forgot to initialize something */
-    memset (p + len, 0, len4 - len);
-  }
+  /* zero out padding bytes added to satisfy parameter alignment: this way
+     valgrind can tell us where we forgot to initialize something */
+  while (len < len4)
+    p[len++] = 0;
   return p;
 }