diff --git a/gatk.wdl b/gatk.wdl
index 8107d1e40b8c70cfb911125e321f0accc64c38d4..56e2bd4011468223c61713ad161374b269b36861 100644
--- a/gatk.wdl
+++ b/gatk.wdl
@@ -278,7 +278,7 @@ task SplitNCigarReads {
 
     output {
         File bam = output_bam
-        File bam_index = output_bam + ".bai"
+        File bam_index = sub(output_bam, ".bam$", ".bai")
     }
 
     runtime {