diff --git a/dge_workflow/dge_utils.sh b/dge_workflow/dge_utils.sh
index dadb9ce674dab4a856d70dc2d7c823dd2beb1e05..16e697dfb31fff467feec82fd2375a1ca243650f 100755
--- a/dge_workflow/dge_utils.sh
+++ b/dge_workflow/dge_utils.sh
@@ -414,6 +414,12 @@ dge_create_star_index(){
     fi
 
     export star_index="${igenome}/Sequence/StarIndex"
+
+    ## stop if index exists already
+    if [ -d "$star_index" ]; then
+        echo "Error: Index directory ${star_index} already exists." >&2 ; return;
+    fi
+
     chmod +w $(dirname ${star_index})
 
     mailme "${project}: creating STAR index in ${star_index}"