diff --git a/bam2bigwig.sh b/bam2bigwig.sh
index c26e64fab78e50758870a3d01344a4255c148a3a..2534b051e01e518a6595f214d197078ee1dd3208 100755
--- a/bam2bigwig.sh
+++ b/bam2bigwig.sh
@@ -82,7 +82,7 @@ then
     if [ -f ${norm} ]
     then
         echo "reading scaling factor for ${lib_name} in ${norm}"
-        size=$(grep "${lib_name}" ${norm} | cut -f2)
+        size=$(grep -w "^${lib_name}" ${norm} | cut -f2)
         if [ ! ${size} ]
         then
             error_exit "size could not be found on column 2, line ${lib_name} of ${norm}"