diff --git a/c_gen/c_match.py b/c_gen/c_match.py
index 0da5227..d7fa178 100644
--- a/c_gen/c_match.py
+++ b/c_gen/c_match.py
@@ -873,7 +873,8 @@
                 of_match_v%(version)s_delete(wire_match);
                 return rv;
             }
-            octets->bytes = OF_MATCH_BYTES(wire_match->length);
+            of_wire_buffer_grow(wire_match->wbuf, OF_MATCH_BYTES(wire_match->length));
+            octets->bytes = wire_match->wbuf->current_bytes;
             of_object_wire_buffer_steal((of_object_t *)wire_match,
                                         &octets->data);
             of_match_v%(version)s_delete(wire_match);
diff --git a/c_gen/templates/of_wire_buf.h b/c_gen/templates/of_wire_buf.h
index 0723454..ec65098 100644
--- a/c_gen/templates/of_wire_buf.h
+++ b/c_gen/templates/of_wire_buf.h
@@ -174,7 +174,6 @@
         FREE(wbuf);
         return NULL;
     }
-    MEMSET(wbuf->buf, 0, a_bytes);
     wbuf->current_bytes = 0;
     wbuf->alloc_bytes = a_bytes;
 
@@ -245,6 +244,7 @@
     LOCI_ASSERT(wbuf != NULL);
     LOCI_ASSERT(wbuf->alloc_bytes >= bytes);
     if (bytes > wbuf->current_bytes) {
+        MEMSET(wbuf->buf + wbuf->current_bytes, 0, bytes - wbuf->current_bytes);
         wbuf->current_bytes = bytes;
     }
 }