diff --git a/src/nf_modules/bwa/main.nf b/src/nf_modules/bwa/main.nf
index 1fd03feb8b1402477876deb8f482b6089514bc8a..11aac6062f2c2eb2317073862cb273361c59c257 100644
--- a/src/nf_modules/bwa/main.nf
+++ b/src/nf_modules/bwa/main.nf
@@ -49,10 +49,13 @@ process mapping_fastq {
   if (file_id instanceof List){
     library = file_id[0]
     file_prefix = file_id[0]
-    if (file_id.containsKey('library')) {
-      library = file_id.library
-      file_prefix = file_id.id
-    }
+  } else if (file_id instanceof Map)
+      library = file_id[0]
+      file_prefix = file_id[0]
+      if (file_id.containsKey('library')) {
+        library = file_id.library
+        file_prefix = file_id.id
+      }
   } else {
     library = file_id
     file_prefix = file_id