diff --git a/nomad/app/flask/api/materialtransformer.py b/nomad/app/flask/api/materialtransformer.py
index 3d50ca50352d0a879611893e68a0657561e31ebc..cbae16f292e0f9b8854c6fbb118f961290839555 100644
--- a/nomad/app/flask/api/materialtransformer.py
+++ b/nomad/app/flask/api/materialtransformer.py
@@ -1,6 +1,6 @@
 from typing import Callable
 from lark import v_args
-from elasticsearch_dsl import Q, Field
+from elasticsearch_dsl import Q, Field, Text, Keyword, Integer, Boolean
 from optimade.filtertransformers.elasticsearch import Quantity
 from nomad.atomutils import get_hill_decomposition
 
@@ -69,7 +69,8 @@ class MElasticTransformer(ElasticTransformer):
     A specialized Optimade/Lark transformer for handling material queries.
     Provides mostly the same functionality as
     optimade.filtertransformers.elasticsearch.ElasticTransformer, but has
-    additions that make nested queries and parameter conversions possible.
+    additions that make nested queries, parameter conversions and the use of
+    boolean values possible.
 
     Uses elasticsearch_dsl and will produce a :class:`Q` instance.
 
@@ -77,6 +78,29 @@ class MElasticTransformer(ElasticTransformer):
         quantities: A list of :class:`MQuantity`s that describe how optimade (and other)
             quantities are mapped to the elasticsearch index.
     '''
+    def _query_op(self, quantity, op, value, nested=None):
+        """
+        Return a range, match, or term query for the given quantity, comparison
+        operator, and value
+        """
+        field = self._field(quantity, nested=nested)
+        if op in _cmp_operators:
+            return Q("range", **{field: {_cmp_operators[op]: value}})
+
+        if quantity.elastic_mapping_type == Text:
+            query_type = "match"
+        elif quantity.elastic_mapping_type in [Keyword, Integer, Boolean]:
+            query_type = "term"
+        else:
+            raise NotImplementedError("Quantity has unsupported ES field type")
+
+        if op in ["=", ""]:
+            return Q(query_type, **{field: value})
+
+        if op == "!=":
+            return ~Q(  # pylint: disable=invalid-unary-operand-type
+                query_type, **{field: value}
+            )
 
     def _has_query_op(self, quantities, op, predicate_zip_list):
         """
diff --git a/tests/app/flask/test_api_encyclopedia.py b/tests/app/flask/test_api_encyclopedia.py
index b83554dfe62c18022d8622b15ee8e7b853e5310f..ab64ac54ed2948dd7c57b466e15c24e2c8b8b6f7 100644
--- a/tests/app/flask/test_api_encyclopedia.py
+++ b/tests/app/flask/test_api_encyclopedia.py
@@ -403,12 +403,33 @@ class TestEncyclopedia():
         # Test that invalid query parameters raise code 400
 
     def test_complex_search(self, enc_upload, elastic_infra, api, test_user_auth):
+        # Test an elaborate boolean query for elements
+        query = json.dumps({"query": """(
+          ( elements HAS ALL "Si", "O" OR elements HAS ALL "Ge", "O" ) OR
+          ( elements HAS ALL "Si", "N" OR elements HAS ALL "Ge", "N" )
+        )"""})
+        rv = api.post('/materials/', data=query, content_type='application/json')
+        assert rv.status_code == 200
+        results = rv.json['results']
+        assert len(results) == 0
+
+        # Test that there are no issues with the custom Optimade grammar
+        # containing boolean values. See discussion at
+        # https://github.com/Materials-Consortia/OPTIMADE/issues/345
+        query = json.dumps({"query": 'has_band_structure=TRUE'})
+        rv = api.post('/materials/', data=query, content_type='application/json')
+        assert rv.status_code == 200
+        results = rv.json['results']
+        assert len(results) == 1
+
         # Test that completely private materials only become visible after
         # authentication
         query = json.dumps({"query": 'elements HAS ALL "B"'})
         rv = api.post('/materials/', data=query, content_type='application/json')
         results = rv.json['results']
+        assert rv.status_code == 200
         assert len(results) == 0
         rv = api.post('/materials/', data=query, content_type='application/json', headers=test_user_auth)
+        assert rv.status_code == 200
         results = rv.json['results']
         assert len(results) == 1