diff --git a/syncapi/storage/filtering.go b/syncapi/storage/filtering.go
index 75fc595e0..4ac88a219 100644
--- a/syncapi/storage/filtering.go
+++ b/syncapi/storage/filtering.go
@@ -22,6 +22,12 @@ import (
 // https://matrix.org/docs/spec/client_server/r0.3.0.html#post-matrix-client-r0-user-userid-filter
 // to SQL wildcards that can be used with LIKE()
 func filterConvertTypeWildcardToSQL(values []string) []string {
+	if len(values) == 0 {
+		// Return nil instead of []string{} so IS NULL can work correctly when
+		// the return value is passed into SQL queries
+		return nil
+	}
+
 	ret := make([]string, len(values))
 	for i := range values {
 		ret[i] = strings.Replace(values[i], "*", "%", -1)