diff --git a/README.md b/README.md
index e140d68..22bc37f 100644
--- a/README.md
+++ b/README.md
@@ -59,23 +59,23 @@ Call the attributes, for example
 
 ## Documentation
 
-| Field                     | EpiDoc source element (XPath)                                                  |
-|---------------------------|--------------------------------------------------------------------------------|
-| commentary                | `//body/div[@type='commentary' and @subtype='general']`                        |
-| edition_foreign_languages | `//body/div[@type='edition']//foreign/@xml:lang`                               |
-| edition_language          | `//body/div[@type='edition']/@xml:lang`                                        |
-| idno                      | `//teiHeader/fileDesc/publicationStmt/idno`                                    |
-| authority                 | `//teiHeader/fileDesc/publicationStmt/authority`                               |
-| availability              | `//teiHeader/fileDesc/publicationStmt/availability`                            |
-| languages                 | `//teiHeader/profileDesc/langUsage/language`                                   |
-| material                  | `//teiHeader/fileDesc/sourceDesc/msDesc/physDesc/objectDesc//support/material` |
-| origin_dates              | `//teiHeader/fileDesc/sourceDesc/msDesc/history/origin/origDate`               |
-| origin_place              | `//teiHeader/fileDesc/sourceDesc/msDesc/history/origin/origPlace`              |
-| provenances               | `//teiHeader/fileDesc/sourceDesc/msDesc/history/provenance`                    |
-| reprint_from              | `//body/ref[@type='reprint-from']`                                             |
-| reprint_in                | `//body/ref[@type='reprint-in']`                                               |
-| terms                     | `//teiHeader/profileDesc/textClass//term`                                      |
-| title                     | `//teiHeader/fileDesc/titleStmt/title`                                         |
+| Field                     | EpiDoc source element (XPath)                                                                          |
+|---------------------------|--------------------------------------------------------------------------------------------------------|
+| commentary                | `//body/div[@type='commentary' and @subtype='general']`                                                |
+| edition_foreign_languages | `//body/div[@type='edition']//foreign/@xml:lang`                                                       |
+| edition_language          | `//body/div[@type='edition']/@xml:lang`                                                                |
+| idno                      | `//teiHeader/fileDesc/publicationStmt/idno` `//teiHeader/fileDesc/sourceDesc/msDesc/msIdentifier/idno` |
+| authority                 | `//teiHeader/fileDesc/publicationStmt/authority`                                                       |
+| availability              | `//teiHeader/fileDesc/publicationStmt/availability`                                                    |
+| languages                 | `//teiHeader/profileDesc/langUsage/language`                                                           |
+| material                  | `//teiHeader/fileDesc/sourceDesc/msDesc/physDesc/objectDesc//support/material`                         |
+| origin_dates              | `//teiHeader/fileDesc/sourceDesc/msDesc/history/origin/origDate`                                       |
+| origin_place              | `//teiHeader/fileDesc/sourceDesc/msDesc/history/origin/origPlace`                                      |
+| provenances               | `//teiHeader/fileDesc/sourceDesc/msDesc/history/provenance`                                            |
+| reprint_from              | `//body/ref[@type='reprint-from']`                                                                     |
+| reprint_in                | `//body/ref[@type='reprint-in']`                                                                       |
+| terms                     | `//teiHeader/profileDesc/textClass//term`                                                              |
+| title                     | `//teiHeader/fileDesc/titleStmt/title`                                                                 |
 
 ## Development
 
diff --git a/epidoc_parser/api.py b/epidoc_parser/api.py
index ab0046b..853f86c 100644
--- a/epidoc_parser/api.py
+++ b/epidoc_parser/api.py
@@ -116,6 +116,12 @@ def loads(s: str) -> EpiDoc:
     if sourcedesc:
         msdesc = sourcedesc.msdesc
         if msdesc:
+            msidentifier = msdesc.msidentifier
+            if msidentifier:
+                idno = msidentifier.idno
+                if idno and hasattr(idno, "type"):
+                    if idno.get("type") == "invNo":
+                        doc.idno["invno"] = idno.text
             physdesc = msdesc.physdesc
             if physdesc:
                 objectdesc = physdesc.objectdesc
diff --git a/tests/test_api.py b/tests/test_api.py
index 22b6f65..aa26e01 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -46,7 +46,13 @@ def test_all(self):
                 os.path.join("apis", "yale.apis.0000540000.xml"),
                 EpiDoc.create(
                     title="Receipt, Roman CE ii (ca. 162) [BPG]",
-                    idno={"apisid": "yale.apis.0000540000", "controlno": "(cty)54", "hgv": "20671", "tm": "20671"},
+                    idno={
+                        "apisid": "yale.apis.0000540000",
+                        "controlno": "(cty)54",
+                        "hgv": "20671",
+                        "invno": "P.CtYBR inv. 54",
+                        "tm": "20671",
+                    },
                     authority="APIS",
                     origin_dates=[{"notafter": "0199", "notbefore": "0100", "text": "Roman CE ii (ca. 162) [BPG]"}],
                     terms=[{"text": "Receipt"}, {"text": "Papyri"}],
@@ -95,6 +101,7 @@ def test_all(self):
                         "dclp": "26761",
                         "dclp-hybrid": "sb;16;13045",
                         "filename": "26761",
+                        "invno": "Vienna, Nationalbibliothek G 39978",
                         "ldab": "5148",
                         "tm": "26761",
                     },
@@ -143,6 +150,7 @@ def test_all(self):
                         "dclp": "135858",
                         "dclp-hybrid": "tm;;135858",
                         "filename": "135858",
+                        "invno": "Cairo, Coptic Museum 901",
                         "ldab": "135858",
                         "tm": "135858",
                     },