diff --git a/workflows/differentialabundance.nf b/workflows/differentialabundance.nf
index 216384bc..c235797f 100644
--- a/workflows/differentialabundance.nf
+++ b/workflows/differentialabundance.nf
@@ -56,8 +56,8 @@ if (params.study_type == 'affy_array'){
 }
 
 // Check optional parameters
-if (params.transcript_length_matrix) { ch_transcript_lengths = Channel.of([ exp_meta, file(params.transcript_length_matrix, checkIfExists: true)]).first() } else { ch_transcript_lengths = [[],[]] }
-if (params.control_features) { ch_control_features = Channel.of([ exp_meta, file(params.control_features, checkIfExists: true)]).first() } else { ch_control_features = [[],[]] }
+if (params.transcript_length_matrix) { ch_transcript_lengths = Channel.of([ exp_meta, file(params.transcript_length_matrix, checkIfExists: true)]).first() } else { ch_transcript_lengths = Channel.of([[],[]]) }
+if (params.control_features) { ch_control_features = Channel.of([ exp_meta, file(params.control_features, checkIfExists: true)]).first() } else { ch_control_features = Channel.of([[],[]]) }
 
 def run_gene_set_analysis = params.gsea_run || params.gprofiler2_run