diff --git a/src/calibre/ebooks/pdf/html_writer.py b/src/calibre/ebooks/pdf/html_writer.py
index 08d203cd4b..623e914898 100644
--- a/src/calibre/ebooks/pdf/html_writer.py
+++ b/src/calibre/ebooks/pdf/html_writer.py
@@ -1134,7 +1134,7 @@ def convert(opf_path, opts, metadata=None, output_path=None, log=default_log, co
     results = manager.convert_html_files(jobs, settle_time=1, has_maths=has_maths)
     num_pages = 0
     page_margins_map = []
-    log(f'Merging {len(margin_files)} PDF render results, this could take a while...')
+    all_docs = []
     for i, margin_file in enumerate(margin_files):
         name = margin_file.name
         data = results[name]
@@ -1145,13 +1145,10 @@ def convert(opf_path, opts, metadata=None, output_path=None, log=default_log, co
         doc_pages = doc.page_count()
         page_margins_map.extend(repeat(resolve_margins(margin_file.margins, page_layout), doc_pages))
         num_pages += doc_pages
+        all_docs.append(doc)
 
-        if pdf_doc is None:
-            pdf_doc = doc
-        else:
-            st = monotonic()
-            pdf_doc.append(doc)
-            log(f'Merged ({i}/{len(margin_files)-1}) in {monotonic()-st:.1f} seconds')
+    pdf_doc = all_docs[0]
+    pdf_doc.append(*all_docs[1:])
 
     page_number_display_map = get_page_number_display_map(manager, opts, num_pages, log)
 
diff --git a/src/calibre/utils/podofo/doc.cpp b/src/calibre/utils/podofo/doc.cpp
index 6f1220c9b9..66a6499bde 100644
--- a/src/calibre/utils/podofo/doc.cpp
+++ b/src/calibre/utils/podofo/doc.cpp
@@ -11,6 +11,7 @@
 #include <new>
 #include <string_view>
 #include <unordered_map>
+#include <vector>
 
 using namespace pdf;
 
@@ -365,12 +366,15 @@ PDFDoc_append(PDFDoc *self, PyObject *args) {
     PdfMemDocument *dest = self->doc;
 
     try {
+        std::vector<const PdfMemDocument*> docs(PyTuple_GET_SIZE(args));
         for (Py_ssize_t i = 0; i < PyTuple_GET_SIZE(args); i++) {
             PyObject *doc = PyTuple_GET_ITEM(args, i);
             int typ = PyObject_IsInstance(doc, (PyObject*)&PDFDocType);
             if (typ == -1) return NULL;
             if (typ == 0) { PyErr_SetString(PyExc_TypeError, "You must pass a PDFDoc instance to this method"); return NULL; }
-            const PdfMemDocument *src = ((PDFDoc*)doc)->doc;
+            docs[i] = ((PDFDoc*)doc)->doc;
+        }
+        for (auto src : docs) {
             std::unordered_map<PdfReference, PdfObject*> ref_map;
             std::unordered_map<PdfReference, PdfReference> page_parent_map;
             const unsigned initial_page_count = dest->GetPages().GetCount();