diff --git a/src/config.rs b/src/config.rs
index db159a45..7ef8bcef 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -421,6 +421,9 @@ pub struct BookConfig {
     /// Location of the book source relative to the book's root directory.
     pub src: PathBuf,
     /// Does this book support more than one language?
+    // TODO: Remove this field in 0.5, it is unused:
+    // https://github.com/rust-lang/mdBook/issues/2636
+    #[serde(skip_serializing)]
     pub multilingual: bool,
     /// The main language of the book.
     pub language: Option<String>,
diff --git a/tests/testsuite/init.rs b/tests/testsuite/init.rs
index a5e1e28b..e5989eb6 100644
--- a/tests/testsuite/init.rs
+++ b/tests/testsuite/init.rs
@@ -28,7 +28,6 @@ All done, no errors...
 [book]
 authors = []
 language = "en"
-multilingual = false
 src = "src"
 
 "#]],
@@ -95,7 +94,6 @@ All done, no errors...
 [book]
 authors = []
 language = "en"
-multilingual = false
 src = "src"
 
 "#]],
@@ -129,7 +127,6 @@ All done, no errors...
 [book]
 authors = []
 language = "en"
-multilingual = false
 src = "src"
 title = "Example title"
 
@@ -182,7 +179,6 @@ fn init_with_custom_book_and_src_locations() {
 [book]
 authors = []
 language = "en"
-multilingual = false
 src = "in"
 
 [build]
diff --git a/tests/testsuite/renderer.rs b/tests/testsuite/renderer.rs
index e893dd2f..1e162447 100644
--- a/tests/testsuite/renderer.rs
+++ b/tests/testsuite/renderer.rs
@@ -188,7 +188,6 @@ fn backends_receive_render_context_via_stdin() {
     "book": {
       "authors": [],
       "language": "en",
-      "multilingual": false,
       "src": "src"
     },
     "output": {