diff --git a/services/search/pkg/opensearch/backend.go b/services/search/pkg/opensearch/backend.go
index 24936217ac..000b24ebf1 100644
--- a/services/search/pkg/opensearch/backend.go
+++ b/services/search/pkg/opensearch/backend.go
@@ -9,6 +9,7 @@ import (
 	storageProvider "github.com/cs3org/go-cs3apis/cs3/storage/provider/v1beta1"
 	opensearchgoAPI "github.com/opensearch-project/opensearch-go/v4/opensearchapi"
 
+	"github.com/opencloud-eu/reva/v2/pkg/errtypes"
 	"github.com/opencloud-eu/reva/v2/pkg/storagespace"
 	"github.com/opencloud-eu/reva/v2/pkg/utils"
 
@@ -17,6 +18,7 @@ import (
 	searchService "github.com/opencloud-eu/opencloud/protogen/gen/opencloud/services/search/v0"
 	"github.com/opencloud-eu/opencloud/services/search/pkg/opensearch/internal/convert"
 	"github.com/opencloud-eu/opencloud/services/search/pkg/opensearch/internal/osu"
+	searchQuery "github.com/opencloud-eu/opencloud/services/search/pkg/query"
 	"github.com/opencloud-eu/opencloud/services/search/pkg/search"
 )
 
@@ -68,7 +70,10 @@ func NewBackend(index string, client *opensearchgoAPI.Client) (*Backend, error)
 
 func (b *Backend) Search(ctx context.Context, sir *searchService.SearchIndexRequest) (*searchService.SearchIndexResponse, error) {
 	boolQuery, err := convert.KQLToOpenSearchBoolQuery(sir.Query)
-	if err != nil {
+	switch {
+	case searchQuery.IsValidationError(err):
+		return nil, errtypes.BadRequest(err.Error())
+	case err != nil:
 		return nil, fmt.Errorf("failed to convert KQL query to OpenSearch bool query: %w", err)
 	}
 
diff --git a/services/search/pkg/opensearch/backend_test.go b/services/search/pkg/opensearch/backend_test.go
index 74b41fa674..a8579180ac 100644
--- a/services/search/pkg/opensearch/backend_test.go
+++ b/services/search/pkg/opensearch/backend_test.go
@@ -11,6 +11,8 @@ import (
 	opensearchgo "github.com/opensearch-project/opensearch-go/v4"
 	opensearchgoAPI "github.com/opensearch-project/opensearch-go/v4/opensearchapi"
 
+	"github.com/opencloud-eu/reva/v2/pkg/errtypes"
+
 	searchService "github.com/opencloud-eu/opencloud/protogen/gen/opencloud/services/search/v0"
 	"github.com/opencloud-eu/opencloud/services/search/pkg/opensearch"
 	opensearchtest "github.com/opencloud-eu/opencloud/services/search/pkg/opensearch/internal/test"
@@ -595,4 +597,17 @@ var _ = Describe("Backend", func() {
 		)
 	})
 
+	Describe("SearchWithAnInvalidQuery", func() {
+		const indexName = "opencloud-test-engine-search-invalid-query"
+
+		It("answers with a bad request", func() {
+			backend, tc := newBackend(indexName)
+			deleteIndexOnCleanup(tc, indexName)
+
+			_, err := backend.Search(context.Background(), &searchService.SearchIndexRequest{Query: "AND mediatype:document"})
+			Expect(err).To(HaveOccurred())
+			Expect(err).To(BeAssignableToTypeOf(errtypes.BadRequest("")))
+			Expect(err.Error()).To(Equal(`error: bad request: the expression can't begin from a binary operator: 'AND'`))
+		})
+	})
 })
diff --git a/services/search/pkg/opensearch/internal/convert/kql_query.go b/services/search/pkg/opensearch/internal/convert/kql_query.go
index f04e577077..f824990e6d 100644
--- a/services/search/pkg/opensearch/internal/convert/kql_query.go
+++ b/services/search/pkg/opensearch/internal/convert/kql_query.go
@@ -14,7 +14,7 @@ var (
 func KQLToOpenSearchBoolQuery(kqlQuery string) (*osu.BoolQuery, error) {
 	kqlAst, err := kql.Builder{}.Build(kqlQuery)
 	if err != nil {
-		return nil, fmt.Errorf("failed to build query: %w", err)
+		return nil, err
 	}
 
 	kqlNodes, err := ExpandKQL(kqlAst.Nodes)
diff --git a/services/search/pkg/query/error.go b/services/search/pkg/query/error.go
index a25148d977..27fde9541e 100644
--- a/services/search/pkg/query/error.go
+++ b/services/search/pkg/query/error.go
@@ -1,6 +1,7 @@
 package query
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/opencloud-eu/opencloud/pkg/ast"
@@ -38,10 +39,16 @@ func (e UnsupportedTimeRangeError) Error() string {
 	return fmt.Sprintf("unable to convert '%v' to a time range", e.Value)
 }
 
+// IsValidationError says whether the query itself is at fault, which makes it a
+// bad request and not an error of ours.
 func IsValidationError(err error) bool {
-	switch err.(type) {
-	case *StartsWithBinaryOperatorError, *NamedGroupInvalidNodesError, *UnsupportedTimeRangeError:
-		return true
-	}
-	return false
+	var (
+		startsWithBinaryOperator *StartsWithBinaryOperatorError
+		namedGroupInvalidNodes   *NamedGroupInvalidNodesError
+		unsupportedTimeRange     *UnsupportedTimeRangeError
+	)
+
+	return errors.As(err, &startsWithBinaryOperator) ||
+		errors.As(err, &namedGroupInvalidNodes) ||
+		errors.As(err, &unsupportedTimeRange)
 }