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;
     }
 }