diff --git a/content/booklets/adacore-technologies-for-railway-software/index.rst b/content/booklets/adacore-technologies-for-railway-software/index.rst
index cd6ee4dee..f7a541c6e 100644
--- a/content/booklets/adacore-technologies-for-railway-software/index.rst
+++ b/content/booklets/adacore-technologies-for-railway-software/index.rst
@@ -139,6 +139,8 @@ software, please visit :footcite:`Railway_SW_AdaCore_Web_Rail`.
 | Ben Brosgol, AdaCore
 | September 2025
 
+.. footbibliography::
+
 .. toctree::
    :maxdepth: 4
    :numbered:
diff --git a/content/index.rst b/content/index.rst
index ecd6ca420..01e8d97d1 100644
--- a/content/index.rst
+++ b/content/index.rst
@@ -126,15 +126,13 @@
         Introduction to Ada: Laboratories <labs/intro-to-ada/index>
         Bug Free Coding <labs/bug-free-coding/index>
 
-    .. only:: no_hidden_books
-
-        .. toctree::
-            :maxdepth: 1
-            :caption: AdaCore Technologies Booklets
+    .. toctree::
+        :maxdepth: 1
+        :caption: AdaCore Technologies Booklets
 
-            AdaCore Technologies For Airborne Software <booklets/adacore-technologies-for-airborne-software/index>
-            AdaCore Technologies For Railway Software <booklets/adacore-technologies-for-railway-software/index>
-            AdaCore Technologies For Space Systems Software <booklets/adacore-technologies-for-space-systems-software/index>
+        AdaCore Technologies For Airborne Software <booklets/adacore-technologies-for-airborne-software/index>
+        AdaCore Technologies For Railway Software <booklets/adacore-technologies-for-railway-software/index>
+        AdaCore Technologies For Space Systems Software <booklets/adacore-technologies-for-space-systems-software/index>
 
 .. only:: builder_html
 
diff --git a/frontend/Makefile b/frontend/Makefile
index 4b2b6a8c9..b0df5236b 100644
--- a/frontend/Makefile
+++ b/frontend/Makefile
@@ -212,7 +212,7 @@ test_engine: webpack-production                                                #
 	@echo ""
 
 test_parser:                                                                   ## Test the parser.
-	@coverage run --source=widget,rst_code_example_pipeline.chop,rst_code_example_pipeline.resource -m unittest discover --start-directory sphinx
+	@coverage run --source=widget,footnote_checks,rst_code_example_pipeline.chop,rst_code_example_pipeline.resource -m unittest discover --start-directory sphinx
 	@coverage report --fail-under=90 -m
 
 test_rst_pipeline:                                                             ## Test the rst_code_example_pipeline package (epub VM).
@@ -352,7 +352,7 @@ define build_complete_book
 	$(eval TARGET_TYPE_LC := $(call lowercase_word,$(TARGET_TYPE)))
 	@rm -rf "$(BUILDDIR)/doctrees"
 	$(eval SPHINX_CONTENT_DIR := $(CONTENT_DIR))
-	$(call build_book_complete_preps_$(TARGET_TYPE_LC))
+	$(call build_complete_book_preps_$(TARGET_TYPE_LC))
 	$(call build_book_generic,$(TARGET_NAME),$(TARGET_TYPE),$(SPHINX_CONTENT_DIR))
 endef
 
diff --git a/frontend/sphinx/conf.py b/frontend/sphinx/conf.py
index 84693db65..70d5bafc0 100644
--- a/frontend/sphinx/conf.py
+++ b/frontend/sphinx/conf.py
@@ -104,6 +104,7 @@ def get_file_from_conf_ini(path_to_file):
     'sphinx.ext.graphviz',
     'sphinx.ext.extlinks',
     'widget_extension',
+    'footnote_checks',
     'sphinx_reredirects',
     'sphinxcontrib.plantuml',
 ]
diff --git a/frontend/sphinx/footnote_checks.py b/frontend/sphinx/footnote_checks.py
new file mode 100644
index 000000000..a5ecbf692
--- /dev/null
+++ b/frontend/sphinx/footnote_checks.py
@@ -0,0 +1,51 @@
+"""Reject footnote references whose definitions are absent from the output."""
+
+from docutils import nodes
+from sphinx.errors import SphinxError
+from sphinx.transforms.post_transforms import SphinxPostTransform
+
+
+class CheckFootnoteDefinitions(SphinxPostTransform):
+    # Check after conditional content is removed, before LaTeX's URL-footnote
+    # numbering can make a missing definition look like a repeated reference.
+    default_priority = 390
+
+    def run(self, **kwargs):
+        current_docname = self.env.current_document.docname
+        definitions = {
+            (footnote.get('docname', current_docname), identifier)
+            for footnote in self.document.findall(nodes.footnote)
+            for identifier in footnote['ids']
+        }
+        for reference in self.document.findall(nodes.footnote_reference):
+            identifier = reference.get('refid')
+            if identifier is None:
+                # Docutils reports references that could not resolve an ID.
+                continue
+            docname = reference.get('docname', current_docname)
+            if (docname, identifier) in definitions:
+                continue
+
+            location = str(self.env.doc2path(docname))
+            ancestor = reference
+            while ancestor is not None:
+                if ancestor.line is not None:
+                    location += f':{ancestor.line}'
+                    break
+                ancestor = ancestor.parent
+            raise SphinxError(
+                f"{location}: footnote reference {identifier!r} has no "
+                "definition in this document. Add the missing footnote "
+                "definition; for :footcite: citations, place "
+                "'.. footbibliography::' after the last citation in the "
+                "document."
+            )
+
+
+def setup(app):
+    app.add_post_transform(CheckFootnoteDefinitions)
+    return {
+        'version': '1.0',
+        'parallel_read_safe': True,
+        'parallel_write_safe': True,
+    }