diff --git a/tools/stats/filtering.xml b/tools/stats/filtering.xml
index b762074d9fc..143c9076aa4 100644
--- a/tools/stats/filtering.xml
+++ b/tools/stats/filtering.xml
@@ -4,7 +4,7 @@
     <edam_operation>operation_0335</edam_operation>
   </edam_operations>
   <command interpreter="python">
-    filtering.py $input $out_file1 "$cond" ${input.metadata.columns} "${input.metadata.column_types}" $header_lines
+    filtering.py $input $out_file1 '$cond' ${input.metadata.columns} "${input.metadata.column_types}" $header_lines
   </command>
   <inputs>
     <param format="tabular" name="input" type="data" label="Filter" help="Dataset missing? See TIP below."/>
@@ -12,10 +12,10 @@
       <validator type="empty_field" message="Enter a valid filtering condition, see syntax and examples below."/>
       <sanitizer>
         <valid initial="string.printable">
-          <remove value="$"/>
+          <remove value="'"/>
         </valid>
         <mapping initial="none">
-          <add source="$" target="\$"/>
+          <add source="'" target="\'"/>
         </mapping>
       </sanitizer>
     </param>