diff --git a/lib/App/Sandy/Simulator.pm b/lib/App/Sandy/Simulator.pm
index 63591989..c07ce0ed 100644
--- a/lib/App/Sandy/Simulator.pm
+++ b/lib/App/Sandy/Simulator.pm
@@ -952,7 +952,7 @@ sub _calculate_number_of_reads {
 
 sub _calculate_parent_count {
 	my ($self, $counter_ref) = @_;
-	return if $self->_has_no_fasta_rtree;
+	return {} if $self->_has_no_fasta_rtree;
 
 	my %parent_count;