diff --git a/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/function/library/FnStringJoin.java b/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/function/library/FnStringJoin.java
index c75ed468d..8b63df36c 100644
--- a/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/function/library/FnStringJoin.java
+++ b/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/function/library/FnStringJoin.java
@@ -98,12 +98,14 @@ private static ISequence<IStringItem> execute(
    * @param items
    *          the items to join in string form
    * @param separator
-   * 		  the optional separator to use between joined items
+   *          the optional separator to use between joined items
    * @return the atomized result
    */
   @NonNull
   public static IStringItem fnStringJoin(@NonNull List<? extends IAnyAtomicItem> items, IStringItem separator) {
-    return IStringItem.valueOf(stringJoin(ObjectUtils.notNull(items.stream()), separator == null ? "" : separator.asString()));
+    return IStringItem
+        .valueOf(stringJoin(items.stream().map(item -> item == null ? "" : IStringItem.cast(item).asString()),
+            separator == null ? "" : separator.asString()));
   }
 
   /**
@@ -113,13 +115,11 @@ public static IStringItem fnStringJoin(@NonNull List<? extends IAnyAtomicItem> i
    * @param items
    *          the items to join in string form
    * @param separator
-   * 		  the optional separator to use between joined items
+   *          the optional separator to use between joined items
    * @return the atomized result
    */
   @NonNull
-  private static String stringJoin(@NonNull Stream<? extends IAnyAtomicItem> items, String separator) {
-    return ObjectUtils.notNull(items
-        .map(item -> item == null ? "" : IStringItem.cast(item).asString())
-        .collect(Collectors.joining(separator)));
+  private static String stringJoin(@NonNull Stream<String> items, String separator) {
+    return ObjectUtils.notNull(items.collect(Collectors.joining(separator)));
   }
 }
diff --git a/core/src/test/java/gov/nist/secauto/metaschema/core/metapath/function/library/FnStringJoinTest.java b/core/src/test/java/gov/nist/secauto/metaschema/core/metapath/function/library/FnStringJoinTest.java
index a3b4b1f4b..c974c3096 100644
--- a/core/src/test/java/gov/nist/secauto/metaschema/core/metapath/function/library/FnStringJoinTest.java
+++ b/core/src/test/java/gov/nist/secauto/metaschema/core/metapath/function/library/FnStringJoinTest.java
@@ -29,11 +29,11 @@ private static Stream<Arguments> provideValues() { // NOPMD - false positive
             string("123456789"),
             "string-join(1 to 9)"),
         Arguments.of(
-                string("123456789"),
-                "string-join(1 to 9, '')"),
+            string("123456789"),
+            "string-join(1 to 9, '')"),
         Arguments.of(
-                string("123456789"),
-                "string-join(1 to 9, ())"),
+            string("123456789"),
+            "string-join(1 to 9, ())"),
         Arguments.of(
             string("Now is the time ..."),
             "string-join(('Now', 'is', 'the', 'time', '...'), ' ')"),
@@ -42,7 +42,10 @@ private static Stream<Arguments> provideValues() { // NOPMD - false positive
             "string-join((), 'separator')"),
         Arguments.of(
             string("1, 2, 3, 4, 5"),
-            "string-join(1 to 5, ', ')")
+            "string-join(1 to 5, ', ')"),
+        Arguments.of(
+            string("123"),
+            "string-join((1, '', 2, 3))")
     // Arguments.of(
     // string("xml:id=\"xyz\""),
     // "let $doc := <doc><chap><section xml:id=\"xyz\"/></chap></doc>\n"