diff --git a/koha-tmpl/intranet-tmpl/prog/en/xslt/MARC21slimUtils.xsl b/koha-tmpl/intranet-tmpl/prog/en/xslt/MARC21slimUtils.xsl
index 7fb14ad515..08c90e0d2e 100644
--- a/koha-tmpl/intranet-tmpl/prog/en/xslt/MARC21slimUtils.xsl
+++ b/koha-tmpl/intranet-tmpl/prog/en/xslt/MARC21slimUtils.xsl
@@ -4,7 +4,7 @@
   xmlns:marc="http://www.loc.gov/MARC21/slim"
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
   xmlns:str="http://exslt.org/strings"
-  exclude-result-prefixes="marc">
+  exclude-result-prefixes="marc str">
   <xsl:include href="MARC21Languages.xsl"/>
 	<xsl:template name="datafield">
 		<xsl:param name="tag"/>
diff --git a/koha-tmpl/opac-tmpl/bootstrap/en/xslt/MARC21slim2OPACResults.xsl b/koha-tmpl/opac-tmpl/bootstrap/en/xslt/MARC21slim2OPACResults.xsl
index 6ef7dad123..4f2776daaa 100644
--- a/koha-tmpl/opac-tmpl/bootstrap/en/xslt/MARC21slim2OPACResults.xsl
+++ b/koha-tmpl/opac-tmpl/bootstrap/en/xslt/MARC21slim2OPACResults.xsl
@@ -6,7 +6,7 @@
   xmlns:items="http://www.koha-community.org/items"
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
   xmlns:str="http://exslt.org/strings"
-  exclude-result-prefixes="marc items">
+  exclude-result-prefixes="marc items str">
     <xsl:import href="MARC21slimUtils.xsl"/>
     <xsl:output method = "html" indent="yes" omit-xml-declaration = "yes" encoding="UTF-8"/>
     <xsl:key name="item-by-status" match="items:item" use="items:status"/>