diff --git a/workflow/rules/alienTrimmer.rules b/workflow/rules/alienTrimmer.rules
index 54004be5727803e290ac7a4f33a31344adc2651d..5be52503fe10a671f5aaa0c6fb9ba3765c986cdd 100755
--- a/workflow/rules/alienTrimmer.rules
+++ b/workflow/rules/alienTrimmer.rules
@@ -59,7 +59,7 @@ rule alienTrimmer:
         # paired end or single end
         if [[ ${{#infiles[@]}} -eq 2 ]];
         then
-            cmd+="-1 ${{infiles[0]}} -2 ${{infiles[1]}} -o out_paired"
+            cmd+=" -1 ${{infiles[0]}} -2 ${{infiles[1]}} -o out_paired"
         else
             cmd+=" -i ${{infiles[0]}} -o out_single"
         fi