diff --git a/src/doc.cpp b/src/doc.cpp
index e79a92b74b0..e1dc8fb97de 100644
--- a/src/doc.cpp
+++ b/src/doc.cpp
@@ -1291,6 +1291,9 @@ void Doc::ConvertToCastOffMensuralDoc(bool castOff)
         m_isMensuralMusicOnly = false;
     }
 
+    // Calling Doc::PrepareData is expected to collect visible scores
+    assert(m_dataPreparationDone);
+
     // Make sure the document is not cast-off
     this->UnCastOffDoc();
 
diff --git a/src/iohumdrum.cpp b/src/iohumdrum.cpp
index 4353e83816a..be58d5bb7ca 100644
--- a/src/iohumdrum.cpp
+++ b/src/iohumdrum.cpp
@@ -31612,6 +31612,7 @@ void HumdrumInput::finalizeDocument(Doc *doc)
     if (m_mens) {
         doc->SetMensuralMusicOnly(true);
         doc->m_notationType = NOTATIONTYPE_mensural;
+        doc->PrepareData();
         doc->ConvertToCastOffMensuralDoc(true);
     }
 }