diff --git a/include/openvswitch/ofpbuf.h b/include/openvswitch/ofpbuf.h
index 1fc4a3a7f..0dfa51ecb 100644
--- a/include/openvswitch/ofpbuf.h
+++ b/include/openvswitch/ofpbuf.h
@@ -292,6 +292,13 @@ static inline bool ofpbuf_oversized(const struct ofpbuf *ofpacts)
     return (char *)ofpbuf_tail(ofpacts) - (char *)ofpacts->header > UINT16_MAX;
 }
 
+/* Truncates the buffer to 'new_size' bytes from the tail end of 'b'. */
+static inline void ofpbuf_truncate(struct ofpbuf *b, size_t new_size)
+{
+    ovs_assert(b->size >= new_size);
+    b->size = new_size;
+}
+
 #ifdef  __cplusplus
 }
 #endif
diff --git a/lib/ofp-actions.c b/lib/ofp-actions.c
index 8a05f7c9c..102abbc23 100644
--- a/lib/ofp-actions.c
+++ b/lib/ofp-actions.c
@@ -9674,7 +9674,7 @@ ofpacts_parse(char *str, const struct ofpact_parse_params *pp,
     uint32_t orig_size = pp->ofpacts->size;
     char *error = ofpacts_parse__(str, pp, allow_instructions, outer_action);
     if (error) {
-        pp->ofpacts->size = orig_size;
+        ofpbuf_truncate(pp->ofpacts, orig_size);
     }
     CONST_CAST(struct ofpact_parse_params *, pp)->depth--;
     return error;
diff --git a/tests/test-ofpbuf.c b/tests/test-ofpbuf.c
index 3d7fab90f..296d308a7 100644
--- a/tests/test-ofpbuf.c
+++ b/tests/test-ofpbuf.c
@@ -24,6 +24,7 @@
 #define BUF_SIZE 100
 #define HDR_OFS 10
 #define MSG_OFS 50
+#define DATA_SIZE 16
 
 static void
 test_ofpbuf_main(int argc OVS_UNUSED, char *argv[] OVS_UNUSED)
@@ -59,6 +60,15 @@ test_ofpbuf_main(int argc OVS_UNUSED, char *argv[] OVS_UNUSED)
     ovs_assert(buf->header == (char *) buf->base + BUF_SIZE + HDR_OFS);
     ovs_assert(buf->msg == (char *) buf->base + BUF_SIZE + MSG_OFS);
 
+    size_t prev_size = buf->size;
+    ofpbuf_put_uninit(buf, DATA_SIZE);
+    ofpbuf_truncate(buf, prev_size);
+    /* Check that everything else is unchanged after truncate. */
+    ovs_assert(!buf->size);
+    ovs_assert((char *) buf->base + BUF_SIZE == buf->data);
+    ovs_assert(buf->header == (char *) buf->base + BUF_SIZE + HDR_OFS);
+    ovs_assert(buf->msg == (char *) buf->base + BUF_SIZE + MSG_OFS);
+
     ofpbuf_delete(buf);
     exit(exit_code);
 }