diff --git a/lib/ofp-actions.c b/lib/ofp-actions.c
index 0874cc46a..11642d1e1 100644
--- a/lib/ofp-actions.c
+++ b/lib/ofp-actions.c
@@ -1384,15 +1384,18 @@ ofpact_to_openflow11(const struct ofpact *a, struct ofpbuf *out)
 /* Converts the ofpacts in 'ofpacts' (terminated by OFPACT_END) into OpenFlow
  * 1.1 actions in 'openflow', appending the actions to any existing data in
  * 'openflow'. */
-void
+size_t
 ofpacts_put_openflow11_actions(const struct ofpact ofpacts[],
                                size_t ofpacts_len, struct ofpbuf *openflow)
 {
     const struct ofpact *a;
+    size_t start_size = openflow->size;
 
     OFPACT_FOR_EACH (a, ofpacts, ofpacts_len) {
         ofpact_to_openflow11(a, openflow);
     }
+
+    return openflow->size - start_size;
 }
 
 void
diff --git a/lib/ofp-actions.h b/lib/ofp-actions.h
index 7c9cb055f..d5497a821 100644
--- a/lib/ofp-actions.h
+++ b/lib/ofp-actions.h
@@ -396,8 +396,8 @@ enum ofperr ofpacts_check(const struct ofpact[], size_t ofpacts_len,
 /* Converting ofpacts to OpenFlow. */
 void ofpacts_put_openflow10(const struct ofpact[], size_t ofpacts_len,
                             struct ofpbuf *openflow);
-void ofpacts_put_openflow11_actions(const struct ofpact[], size_t ofpacts_len,
-                                    struct ofpbuf *openflow);
+size_t ofpacts_put_openflow11_actions(const struct ofpact[], size_t ofpacts_len,
+                                      struct ofpbuf *openflow);
 void ofpacts_put_openflow11_instructions(const struct ofpact[],
                                          size_t ofpacts_len,
                                          struct ofpbuf *openflow);