diff --git a/src/main/java/de/ids_mannheim/korap/query/serialize/QuerySerializer.java b/src/main/java/de/ids_mannheim/korap/query/serialize/QuerySerializer.java
index b2cd727..7f9166e 100644
--- a/src/main/java/de/ids_mannheim/korap/query/serialize/QuerySerializer.java
+++ b/src/main/java/de/ids_mannheim/korap/query/serialize/QuerySerializer.java
@@ -189,8 +189,8 @@
             List errors = (List) requestMap.get("errors");
             List warnings = (List) requestMap.get("warnings");
             List messages = (List) requestMap.get("messages");
-            this.collection = mergeCollection(collection, this.collection);
-            requestMap.put("collection", this.collection);
+            collection = mergeCollection(collection, this.collection);
+            requestMap.put("collection", collection);
             if (this.meta != null) {
                 this.meta.putAll(meta);
                 requestMap.put("meta", this.meta);
@@ -237,6 +237,8 @@
             return collection2;
         }else if (collection2 == null || collection2.isEmpty()) {
             return collection1;
+        }else if (collection1.equals(collection2)) {
+            return collection1;
         }else {
             LinkedHashMap<String, Object> docGroup = KoralObjectGenerator
                     .makeDocGroup("and");
diff --git a/src/test/java/de/ids_mannheim/korap/query/serialize/PoliqarpPlusQueryProcessorTest.java b/src/test/java/de/ids_mannheim/korap/query/serialize/PoliqarpPlusQueryProcessorTest.java
index 344e78c..171f1b3 100644
--- a/src/test/java/de/ids_mannheim/korap/query/serialize/PoliqarpPlusQueryProcessorTest.java
+++ b/src/test/java/de/ids_mannheim/korap/query/serialize/PoliqarpPlusQueryProcessorTest.java
@@ -154,6 +154,17 @@
         assertEquals("type:regex", res.at("/query/wrap/type").asText());
         assertEquals("orth", res.at("/query/wrap/layer").asText());
         assertEquals("match:eq", res.at("/query/wrap/match").asText());
+
+        // Escape regex symbols
+        query = "\"a\\.\"";
+        qs.setQuery(query, "poliqarpplus");
+        res = mapper.readTree(qs.toJSON());
+        assertEquals("koral:token", res.at("/query/@type").asText());
+        assertEquals("koral:term", res.at("/query/wrap/@type").asText());
+        assertEquals("a\\.", res.at("/query/wrap/key").asText());
+        assertEquals("type:regex", res.at("/query/wrap/type").asText());
+        assertEquals("orth", res.at("/query/wrap/layer").asText());
+        assertEquals("match:eq", res.at("/query/wrap/match").asText());
     }