diff --git a/lib/ex_doc/formatter/epub/templates.ex b/lib/ex_doc/formatter/epub/templates.ex
index 2bea6d45c..f88b990c5 100644
--- a/lib/ex_doc/formatter/epub/templates.ex
+++ b/lib/ex_doc/formatter/epub/templates.ex
@@ -8,6 +8,8 @@ defmodule ExDoc.Formatter.EPUB.Templates do
   alias ExDoc.Formatter.HTML.Templates, as: H
   alias ExDoc.Formatter.EPUB.Assets
 
+  defp enc(binary), do: h(URI.encode(binary))
+
   # The actual rendering happens here
   defp render_doc(ast), do: ast && ExDoc.DocAST.to_html(ast)
 
diff --git a/lib/ex_doc/formatter/epub/templates/content_template.eex b/lib/ex_doc/formatter/epub/templates/content_template.eex
index eecaf0d42..248839186 100644
--- a/lib/ex_doc/formatter/epub/templates/content_template.eex
+++ b/lib/ex_doc/formatter/epub/templates/content_template.eex
@@ -18,10 +18,10 @@
     <item id="nav" href="nav.xhtml" media-type="application/xhtml+xml" properties="nav scripted"/>
     <item id="cover" href="title.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
     <%= for extra <- extras do %>
-      <item id="<%= URI.encode extra.id %>" href="<%= URI.encode extra.id %>.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
+      <item id="<%= enc extra.id %>" href="<%= enc extra.id %>.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
     <% end %>
     <%= for node <- modules ++ tasks do %>
-      <item id="<%= URI.encode node.id %>" href="<%= URI.encode node.id %>.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
+      <item id="<%= enc node.id %>" href="<%= enc node.id %>.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
     <% end %>
     <%= for {static_file, media_type} <- static_files do %>
       <item id="<%= static_file_to_id(static_file) %>" href="<%= static_file %>" media-type="<%= media_type %>"/>
@@ -37,10 +37,10 @@
     <itemref idref="cover"/>
     <itemref idref="nav"/>
     <%= for extra <- extras do %>
-      <itemref idref="<%= URI.encode extra.id %>"/>
+      <itemref idref="<%= enc extra.id %>"/>
     <% end %>
     <%= for node <- modules ++ tasks do %>
-      <itemref idref="<%= URI.encode node.id %>"/>
+      <itemref idref="<%= enc node.id %>"/>
     <% end %>
   </spine>
 </package>
diff --git a/lib/ex_doc/formatter/epub/templates/nav_grouped_item_template.eex b/lib/ex_doc/formatter/epub/templates/nav_grouped_item_template.eex
index 67b1d0396..22b87e440 100644
--- a/lib/ex_doc/formatter/epub/templates/nav_grouped_item_template.eex
+++ b/lib/ex_doc/formatter/epub/templates/nav_grouped_item_template.eex
@@ -4,7 +4,7 @@
       <ol>
   <% end %>
   <%= for node <- nodes do %>
-      <li><a href="<%= URI.encode node.id %>.xhtml"><%=h node.title %></a></li>
+      <li><a href="<%= enc node.id %>.xhtml"><%=h node.title %></a></li>
   <% end %>
   <%= if title do %>
       </ol>
diff --git a/test/ex_doc/formatter/epub_test.exs b/test/ex_doc/formatter/epub_test.exs
index b63624314..96f501082 100644
--- a/test/ex_doc/formatter/epub_test.exs
+++ b/test/ex_doc/formatter/epub_test.exs
@@ -66,6 +66,28 @@ defmodule ExDoc.Formatter.EPUBTest do
     assert content =~ ~r{<dc:creator id="author2">Jane Doe</dc:creator>}
   end
 
+  test "escapes ids and hrefs built from a configured filename", %{tmp_dir: tmp_dir} = context do
+    extra = tmp_dir <> "/readme.md"
+    File.write!(extra, "# Hello\n")
+
+    generate_and_unzip(context, config(context, extras: [{extra, filename: "a&b"}]))
+
+    content = File.read!(tmp_dir <> "/epub/OEBPS/content.opf")
+    assert content =~ ~s{<item id="a&amp;b" href="a&amp;b.xhtml"}
+    assert content =~ ~s{<itemref idref="a&amp;b"/>}
+
+    nav = File.read!(tmp_dir <> "/epub/OEBPS/nav.xhtml")
+    assert nav =~ ~s{<a href="a&amp;b.xhtml">}
+
+    # an unescaped & here is a fatal XML error, not a quirk
+    for file <- ["content.opf", "nav.xhtml"] do
+      (tmp_dir <> "/epub/OEBPS/" <> file)
+      |> File.read!()
+      |> :binary.bin_to_list()
+      |> :xmerl_scan.string()
+    end
+  end
+
   test "generates an EPUB file in the default directory", %{tmp_dir: tmp_dir} = context do
     generate(config(context))
     assert File.regular?(tmp_dir <> "/epub/#{config(context)[:project]}.epub")