diff --git a/software/snpsites/main.nf b/software/snpsites/main.nf
index bafa8536..7f39932f 100644
--- a/software/snpsites/main.nf
+++ b/software/snpsites/main.nf
@@ -24,6 +24,7 @@ process SNPSITES {
     path "*.fas"        , emit: fasta
     path "*.sites.txt"  , emit: constant_sites
     path "*.version.txt", emit: version
+    env   CONSTANT_SITES, emit: constant_sites_string
 
     script:
     def software = getSoftwareName(task.process)
@@ -34,6 +35,8 @@ process SNPSITES {
 
     echo \$(snp-sites -C $alignment) > constant.sites.txt
 
+    CONSTANT_SITES=\$(cat constant.sites.txt)
+
     echo \$(snp-sites -V 2>&1) | sed 's/snp-sites //' > ${software}.version.txt
     """
 }