diff --git a/ovsdb/condition.c b/ovsdb/condition.c
index 5a3eb4e8a3f..4911fbf59be 100644
--- a/ovsdb/condition.c
+++ b/ovsdb/condition.c
@@ -550,9 +550,14 @@ ovsdb_condition_diff(struct ovsdb_condition *diff,
                            &b->clauses[j]);
     }
 
-    diff->optimized = a->optimized && b->optimized;
-    if (diff->optimized) {
-        ovsdb_condition_optimize(diff);
+    if (diff->n_clauses) {
+        diff->optimized = a->optimized && b->optimized;
+        if (diff->optimized) {
+            ovsdb_condition_optimize(diff);
+        }
+    } else {
+        free(diff->clauses);
+        diff->clauses = NULL;
     }
 }
 
diff --git a/ovsdb/monitor.c b/ovsdb/monitor.c
index 4ccb51b1a98..d1e466faa48 100644
--- a/ovsdb/monitor.c
+++ b/ovsdb/monitor.c
@@ -824,6 +824,7 @@ ovsdb_monitor_table_condition_update(
     ovsdb_condition_destroy(&mtc->new_condition);
     ovsdb_condition_clone(&mtc->new_condition, &cond);
     ovsdb_condition_destroy(&cond);
+    ovsdb_condition_destroy(&mtc->diff_condition);
     ovsdb_condition_diff(&mtc->diff_condition,
                          &mtc->old_condition, &mtc->new_condition);
     ovsdb_monitor_condition_add_columns(dbmon,
diff --git a/tests/ovsdb-monitor.at b/tests/ovsdb-monitor.at
index 12cd2bc3194..3e1df18a112 100644
--- a/tests/ovsdb-monitor.at
+++ b/tests/ovsdb-monitor.at
@@ -586,6 +586,7 @@ row,action,name,number,_version
   [[]],
   [],
   [[[[["name","==","one"],["name","==","two"]]]],
+   [[[["name","==","two"],["name","==","one"]]]],
    [[[["name","==","one"]]]],
     [[[false]]],
     [[[true]]]])