diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/AbstractTermNode.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/AbstractTermNode.php
index 57aa71ffcc..91201e1668 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/AbstractTermNode.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/AbstractTermNode.php
@@ -13,6 +13,7 @@ abstract class AbstractTermNode extends Node implements TermInterface
     protected $text;
     protected $context;
     private $concepts = [];
+    private $pruned_concepts;
 
     public function __construct($text, Context $context = null)
     {
@@ -22,56 +23,70 @@ abstract class AbstractTermNode extends Node implements TermInterface
 
     public function setConcepts(array $concepts)
     {
+        $this->pruned_concepts = null;
         $this->concepts = $concepts;
     }
 
+    private function getPrunedConcepts()
+    {
+        if ($this->pruned_concepts === null) {
+            $this->pruned_concepts = Concept::pruneNarrowConcepts($this->concepts);
+        }
+        return $this->pruned_concepts;
+    }
+
     protected function buildConceptQueries(QueryContext $context)
     {
-        $concepts = Concept::pruneNarrowConcepts($this->concepts);
-        if (!$concepts) {
+        if (!$this->getPrunedConcepts()) {
             return [];
         }
 
-        $query_builder = function (array $fields) use ($concepts) {
-            $index_fields = [];
-            foreach ($fields as $field) {
-                $index_fields[] = $field->getConceptPathIndexField();
-            }
-            if (!$index_fields) {
-                return null;
-            }
+        $query_builder = function (array $fields) {
+            $concept_queries = $this->buildConceptQueriesForFields($fields);
             $query = null;
-            foreach ($concepts as $concept) {
-                $concept_query = [
-                    'multi_match' => [
-                        'fields'   => $index_fields,
-                        'query'    => $concept->getPath()
-                    ]
-                ];
+            foreach ($concept_queries as $concept_query) {
                 $query = QueryHelper::applyBooleanClause($query, 'should', $concept_query);
             }
             return $query;
         };
 
-        $query = $query_builder($context->getUnrestrictedFields());
-        if (
-            isset($query['bool']) &&
-            isset($query['bool']['should']) &&
-            count($query) === 1 /* no options or must(_not) clauses */
-        ) {
-            $queries = $query['bool']['should'];
-        } else {
-            $queries = [$query];
-        }
+        $queries = $this->buildConceptQueriesForFields($context->getUnrestrictedFields());
 
         $private_fields = $context->getPrivateFields();
-        foreach (QueryHelper::wrapPrivateFieldConceptQueries($private_fields, $query_builder) as $private_field_query) {
+        foreach (QueryHelper::wrapPrivateFieldQueries($private_fields, $query_builder) as $private_field_query) {
             $queries[] = $private_field_query;
         }
 
         return $queries;
     }
 
+    protected function buildConceptQueriesForFields(array $fields)
+    {
+        $concepts = $this->getPrunedConcepts();
+        if (!$concepts) {
+            return [];
+        }
+
+        $index_fields = [];
+        foreach ($fields as $field) {
+            $index_fields[] = $field->getConceptPathIndexField();
+        }
+        if (!$index_fields) {
+            return [];
+        }
+
+        $queries = [];
+        foreach ($concepts as $concept) {
+            $queries[] = [
+                'multi_match' => [
+                    'fields'   => $index_fields,
+                    'query'    => $concept->getPath()
+                ]
+            ];
+        }
+        return $queries;
+    }
+
     public function getValue()
     {
         return $this->text;
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/TextNode.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/TextNode.php
index 042f313a18..a5b126fb2d 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/TextNode.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/TextNode.php
@@ -59,19 +59,31 @@ class TextNode extends AbstractTermNode implements ContextAbleInterface
         };
 
         $unrestricted_fields = $context->getUnrestrictedFields();
-        $unrestricted_fields = Field::filterByValueCompatibility($unrestricted_fields, $this->text);
-        $query = $query_builder($unrestricted_fields);
+        $compatible_unrestricted_fields = Field::filterByValueCompatibility($unrestricted_fields, $this->text);
+        $query = $query_builder($compatible_unrestricted_fields);
 
         $private_fields = $context->getPrivateFields();
-        $private_fields = Field::filterByValueCompatibility($private_fields, $this->text);
-        foreach (QueryHelper::wrapPrivateFieldQueries($private_fields, $query_builder) as $private_field_query) {
+        $compatible_private_fields = Field::filterByValueCompatibility($private_fields, $this->text);
+        foreach (QueryHelper::wrapPrivateFieldQueries($compatible_private_fields, $query_builder) as $private_field_query) {
             $query = QueryHelper::applyBooleanClause($query, 'should', $private_field_query);
         }
 
-        $concept_queries = $this->buildConceptQueries($context);
+        // Concepts handling
+        $concept_queries = $this->buildConceptQueriesForFields($unrestricted_fields);
         foreach ($concept_queries as $concept_query) {
             $query = QueryHelper::applyBooleanClause($query, 'should', $concept_query);
         }
+        $query_builder = function (array $fields) {
+            $concept_queries = $this->buildConceptQueriesForFields($fields);
+            $query = null;
+            foreach ($concept_queries as $concept_query) {
+                $query = QueryHelper::applyBooleanClause($query, 'should', $concept_query);
+            }
+            return $query;
+        };
+        foreach (QueryHelper::wrapPrivateFieldQueries($private_fields, $query_builder) as $private_field_query) {
+            $query = QueryHelper::applyBooleanClause($query, 'should', $private_field_query);
+        }
 
         return $query;
     }
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryHelper.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryHelper.php
index fb2103c3cf..9d652f86c7 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryHelper.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryHelper.php
@@ -29,10 +29,10 @@ class QueryHelper
         foreach ($fields_map as $hash => $fields) {
             // Right to query on a private field is dependant of document collection
             // Here we make sure we can only match on allowed collections
-            $queries[] = self::restrictQueryToCollections(
-                $query_builder($fields),
-                $collections_map[$hash]
-            );
+            $query = $query_builder($fields);
+            if ($query !== null) {
+                $queries[] = self::restrictQueryToCollections($query, $collections_map[$hash]);
+            }
         }
 
         return $queries;
@@ -61,38 +61,6 @@ class QueryHelper
         return implode('|', $collections);
     }
 
-    /**
-     * @todo Factor with wrapPrivateFieldQueries()
-     */
-    public static function wrapPrivateFieldConceptQueries(array $fields, \Closure $query_builder)
-    {
-        // We make a boolean clause for each collection set to shrink query size
-        // (instead of a clause for each field, with his collection set)
-        $fields_map = [];
-        $collections_map = [];
-        foreach ($fields as $field) {
-            $collections = $field->getDependantCollections();
-            $hash = self::hashCollections($collections);
-            $collections_map[$hash] = $collections;
-            if (!isset($fields_map[$hash])) {
-                $fields_map[$hash] = [];
-            }
-            // Merge fields with others having the same collections
-            $fields_map[$hash][] = $field;
-        }
-
-        $queries = [];
-        foreach ($fields_map as $hash => $fields) {
-            // Right to query on a private field is dependant of document collection
-            // Here we make sure we can only match on allowed collections
-            $query = $query_builder($fields);
-            $query = self::restrictQueryToCollections($query, $collections_map[$hash]);
-            $queries[] = $query;
-        }
-
-        return $queries;
-    }
-
     /**
      * Apply conjunction or disjunction between a query and a sub query clause
      *