diff --git a/src/nf_modules/bwa/main.nf b/src/nf_modules/bwa/main.nf
index d427549c7634d1f51eaef59269715b383c038c0d..1fd03feb8b1402477876deb8f482b6089514bc8a 100644
--- a/src/nf_modules/bwa/main.nf
+++ b/src/nf_modules/bwa/main.nf
@@ -49,9 +49,10 @@ process mapping_fastq {
   if (file_id instanceof List){
     library = file_id[0]
     file_prefix = file_id[0]
-  } else if (file_id.containsKey('library')) {
-    library = file_id.library
-    file_prefix = file_id.id
+    if (file_id.containsKey('library')) {
+      library = file_id.library
+      file_prefix = file_id.id
+    }
   } else {
     library = file_id
     file_prefix = file_id