diff --git a/crates/mdbook-core/src/config.rs b/crates/mdbook-core/src/config.rs
index b2c6862c30..8e79d53e51 100644
--- a/crates/mdbook-core/src/config.rs
+++ b/crates/mdbook-core/src/config.rs
@@ -44,7 +44,7 @@
 //! ```
 
 use crate::static_regex;
-use crate::utils::{TomlExt, fs, log_backtrace};
+use crate::utils::{TomlExt, fs};
 use anyhow::{Context, Error, Result, bail};
 use serde::{Deserialize, Serialize};
 use std::collections::{BTreeMap, HashMap};
@@ -247,15 +247,8 @@ impl Config {
     /// This is for compatibility only. It will be removed completely once the
     /// HTML renderer is refactored to be less coupled to `mdbook` internals.
     #[doc(hidden)]
-    pub fn html_config(&self) -> Option<HtmlConfig> {
-        match self.get("output.html") {
-            Ok(Some(config)) => Some(config),
-            Ok(None) => None,
-            Err(e) => {
-                log_backtrace(&e);
-                None
-            }
-        }
+    pub fn html_config(&self) -> Result<Option<HtmlConfig>> {
+        self.get("output.html")
     }
 
     /// Set a config key, clobbering any existing values along the way.
@@ -816,7 +809,7 @@ mod tests {
         assert_eq!(got.book, book_should_be);
         assert_eq!(got.build, build_should_be);
         assert_eq!(got.rust, rust_should_be);
-        assert_eq!(got.html_config().unwrap(), html_should_be);
+        assert_eq!(got.html_config().unwrap().unwrap(), html_should_be);
     }
 
     #[test]
@@ -832,7 +825,7 @@ mod tests {
         "#;
 
         let got = Config::from_str(src).unwrap();
-        assert!(!got.html_config().unwrap().playground.runnable);
+        assert!(!got.html_config().unwrap().unwrap().playground.runnable);
     }
 
     #[test]
@@ -995,7 +988,7 @@ mod tests {
         "#;
 
         let got = Config::from_str(src).unwrap();
-        let html_config = got.html_config().unwrap();
+        let html_config = got.html_config().unwrap().unwrap();
         assert_eq!(html_config.input_404, None);
         assert_eq!(html_config.get_404_output_file(), "404.html");
     }
@@ -1008,7 +1001,7 @@ mod tests {
         "#;
 
         let got = Config::from_str(src).unwrap();
-        let html_config = got.html_config().unwrap();
+        let html_config = got.html_config().unwrap().unwrap();
         assert_eq!(html_config.input_404, Some("missing.md".to_string()));
         assert_eq!(html_config.get_404_output_file(), "missing.html");
     }
@@ -1153,7 +1146,7 @@ mod tests {
         enable = false
         "#;
         let got = Config::from_str(src).unwrap();
-        let html_config = got.html_config().unwrap();
+        let html_config = got.html_config().unwrap().unwrap();
         assert!(!html_config.print.enable);
         assert!(html_config.print.page_break);
         let src = r#"
@@ -1161,7 +1154,7 @@ mod tests {
         page-break = false
         "#;
         let got = Config::from_str(src).unwrap();
-        let html_config = got.html_config().unwrap();
+        let html_config = got.html_config().unwrap().unwrap();
         assert!(html_config.print.enable);
         assert!(!html_config.print.page_break);
     }
@@ -1173,6 +1166,29 @@ mod tests {
         assert_eq!(json!(TextDirection::LeftToRight), json!("ltr"));
     }
 
+    #[test]
+    fn html_config_rejects_unknown_fields() {
+        let src = r#"
+        [book]
+        title = "Some Book"
+
+        [output.html]
+        foo = 123
+        "#;
+
+        let got = Config::from_str(src).unwrap();
+        let err = got.html_config().unwrap_err();
+        let err_msg = format!("{err:#}");
+        assert!(
+            err_msg.contains("Failed to deserialize `output.html`"),
+            "unexpected error: {err_msg}"
+        );
+        assert!(
+            err_msg.contains("unknown field `foo`"),
+            "unexpected error: {err_msg}"
+        );
+    }
+
     #[test]
     fn get_deserialize_error() {
         let src = r#"
diff --git a/crates/mdbook-driver/src/init.rs b/crates/mdbook-driver/src/init.rs
index badd24c58b..bdfb6b9f53 100644
--- a/crates/mdbook-driver/src/init.rs
+++ b/crates/mdbook-driver/src/init.rs
@@ -108,7 +108,7 @@ impl BookBuilder {
     fn copy_across_theme(&self) -> Result<()> {
         debug!("Copying theme");
 
-        let html_config = self.config.html_config().unwrap_or_default();
+        let html_config = self.config.html_config()?.unwrap_or_default();
         Theme::copy_theme(&html_config, &self.root)?;
         Ok(())
     }
diff --git a/crates/mdbook-driver/src/mdbook.rs b/crates/mdbook-driver/src/mdbook.rs
index 45bae41816..c1e9bcecc5 100644
--- a/crates/mdbook-driver/src/mdbook.rs
+++ b/crates/mdbook-driver/src/mdbook.rs
@@ -384,11 +384,12 @@ impl MDBook {
     }
 
     /// Get the directory containing the theme resources for the book.
-    pub fn theme_dir(&self) -> PathBuf {
-        self.config
-            .html_config()
+    pub fn theme_dir(&self) -> Result<PathBuf> {
+        Ok(self
+            .config
+            .html_config()?
             .unwrap_or_default()
-            .theme_dir(&self.root)
+            .theme_dir(&self.root))
     }
 }
 
diff --git a/crates/mdbook-html/src/html_handlebars/hbs_renderer.rs b/crates/mdbook-html/src/html_handlebars/hbs_renderer.rs
index 8edac3cace..9c3076c23a 100644
--- a/crates/mdbook-html/src/html_handlebars/hbs_renderer.rs
+++ b/crates/mdbook-html/src/html_handlebars/hbs_renderer.rs
@@ -307,7 +307,7 @@ impl Renderer for HtmlHandlebars {
 
     fn render(&self, ctx: &RenderContext) -> Result<()> {
         let book_config = &ctx.config.book;
-        let html_config = ctx.config.html_config().unwrap_or_default();
+        let html_config = ctx.config.html_config()?.unwrap_or_default();
         let src_dir = ctx.root.join(&ctx.config.book.src);
         let destination = &ctx.destination;
         let book = &ctx.book;
diff --git a/crates/mdbook-html/src/html_handlebars/search.rs b/crates/mdbook-html/src/html_handlebars/search.rs
index 09920d76d2..75d693f046 100644
--- a/crates/mdbook-html/src/html_handlebars/search.rs
+++ b/crates/mdbook-html/src/html_handlebars/search.rs
@@ -337,7 +337,7 @@ fn chapter_settings_priority() {
         "foo" = {} # Just to make sure empty table is allowed.
     "#;
     let cfg: mdbook_core::config::Config = toml::from_str(cfg).unwrap();
-    let html = cfg.html_config().unwrap();
+    let html = cfg.html_config().unwrap().unwrap();
     let chapter_configs = sort_search_config(&html.search.unwrap().chapter);
     for (path, enable) in [
         ("foo.md", None),
diff --git a/src/cmd/serve.rs b/src/cmd/serve.rs
index 255c077d98..ec781b395d 100644
--- a/src/cmd/serve.rs
+++ b/src/cmd/serve.rs
@@ -74,7 +74,7 @@ pub fn execute(args: &ArgMatches) -> Result<()> {
         .next()
         .ok_or_else(|| anyhow::anyhow!("no address found for {}", address))?;
     let build_dir = book.build_dir_for("html");
-    let html_config = book.config.html_config().unwrap_or_default();
+    let html_config = book.config.html_config()?.unwrap_or_default();
     let file_404 = html_config.get_404_output_file();
 
     // A channel used to broadcast to any websockets to reload when a file changes.
diff --git a/src/cmd/watch/native.rs b/src/cmd/watch/native.rs
index b4cbc9a774..5c87193637 100644
--- a/src/cmd/watch/native.rs
+++ b/src/cmd/watch/native.rs
@@ -38,7 +38,11 @@ pub fn rebuild_on_change(
         std::process::exit(1);
     };
 
-    let _ = watcher.watch(&book.theme_dir(), Recursive);
+    let theme_dir = book.theme_dir().unwrap_or_else(|e| {
+        error!("invalid book configuration: {e}");
+        std::process::exit(1);
+    });
+    let _ = watcher.watch(&theme_dir, Recursive);
 
     // Add the book.toml file to the watcher if it exists
     let _ = watcher.watch(&book.root.join("book.toml"), NonRecursive);
diff --git a/src/cmd/watch/poller.rs b/src/cmd/watch/poller.rs
index b834b67928..a3c48c71aa 100644
--- a/src/cmd/watch/poller.rs
+++ b/src/cmd/watch/poller.rs
@@ -4,6 +4,7 @@
 //! lots of problems. Various operating systems and different filesystems have
 //! had problems correctly reporting changes.
 
+use anyhow::Result;
 use ignore::gitignore::Gitignore;
 use mdbook_driver::MDBook;
 use pathdiff::diff_paths;
@@ -29,7 +30,10 @@ pub fn rebuild_on_change(
 
     info!("Watching for changes...");
     // Scan once to initialize the starting point.
-    watcher.set_roots(&book);
+    if let Err(e) = watcher.set_roots(&book) {
+        error!("invalid book configuration: {e}");
+        std::process::exit(1);
+    }
     watcher.scan();
 
     // Track average scan time, to help investigate if the poller is taking
@@ -66,7 +70,9 @@ pub fn rebuild_on_change(
                         post_build();
                     }
                     book = b;
-                    watcher.set_roots(&book);
+                    if let Err(e) = watcher.set_roots(&book) {
+                        error!("invalid book configuration: {e}");
+                    }
                 }
                 Err(e) => error!("failed to load book config: {e:?}"),
             }
@@ -121,10 +127,10 @@ impl Watcher {
     }
 
     /// Sets the root directories where scanning will start.
-    fn set_roots(&mut self, book: &MDBook) {
+    fn set_roots(&mut self, book: &MDBook) -> Result<()> {
         let mut root_paths = vec![
             book.source_dir(),
-            book.theme_dir(),
+            book.theme_dir()?,
             book.root.join("book.toml"),
         ];
         root_paths.extend(
@@ -134,7 +140,7 @@ impl Watcher {
                 .iter()
                 .map(|path| book.root.join(path)),
         );
-        if let Some(html_config) = book.config.html_config() {
+        if let Some(html_config) = book.config.html_config()? {
             root_paths.extend(
                 html_config
                     .additional_css
@@ -145,6 +151,7 @@ impl Watcher {
         }
 
         self.root_paths = root_paths;
+        Ok(())
     }
 
     /// Scans for changes.
@@ -276,7 +283,7 @@ mod tests {
         // Create a watcher and check its behavior.
         let book = MDBook::load(&book_root).unwrap();
         let mut watcher = Watcher::new(&book_root);
-        watcher.set_roots(&book);
+        watcher.set_roots(&book).unwrap();
         // Do an initial scan to initialize its state.
         watcher.scan();
         // Verify the steady state is empty.
diff --git a/tests/testsuite/config.rs b/tests/testsuite/config.rs
index 641243c103..7608c14563 100644
--- a/tests/testsuite/config.rs
+++ b/tests/testsuite/config.rs
@@ -179,6 +179,33 @@ ERROR Invalid configuration file
 unknown field `foo`, expected one of `title`, `authors`, `description`, `src`, `language`, `text-direction`
 
 
+"#]]);
+        });
+}
+
+// An invalid key in the HTML output table should fail the build.
+#[test]
+fn bad_config_in_html_table() {
+    BookTest::init(|_| {})
+        .change_file(
+            "book.toml",
+            "[book]\n\
+             title = \"bad-html-config\"\n\
+             \n\
+             [output.html]\n\
+             foo = 123",
+        )
+        .run("build", |cmd| {
+            cmd.expect_failure()
+                .expect_stdout(str![[""]])
+                .expect_stderr(str![[r#"
+ INFO Book building has started
+ INFO Running the html backend
+ERROR Rendering failed
+[TAB]Caused by: Failed to deserialize `output.html`
+[TAB]Caused by: unknown field `foo`, expected one of `theme`, `default-theme`, `preferred-dark-theme`, `smart-punctuation`, `definition-lists`, `admonitions`, `mathjax-support`, `additional-css`, `additional-js`, `fold`, `playground`, `playpen`, `code`, `print`, `no-section-label`, `search`, `git-repository-url`, `git-repository-icon`, `input-404`, `site-url`, `cname`, `edit-url-template`, `live-reload-endpoint`, `redirect`, `hash-files`, `sidebar-header-nav`
+
+
 "#]]);
         });
 }