diff --git a/src/librustdoc/html/render/search_index.rs b/src/librustdoc/html/render/search_index.rs
index f9192a5e648..d672f0bb599 100644
--- a/src/librustdoc/html/render/search_index.rs
+++ b/src/librustdoc/html/render/search_index.rs
@@ -234,7 +234,33 @@ pub(crate) fn build_index<'tcx>(
             )?;
             crate_data.serialize_field(
                 "f",
-                &self.items.iter().map(|item| &item.search_type).collect::<Vec<_>>(),
+                &self
+                    .items
+                    .iter()
+                    .map(|item| {
+                        // Fake option to get `0` out as a sentinel instead of `null`.
+                        // We want to use `0` because it's three less bytes.
+                        enum FunctionOption<'a> {
+                            Function(&'a IndexItemFunctionType),
+                            None,
+                        }
+                        impl<'a> Serialize for FunctionOption<'a> {
+                            fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+                            where
+                                S: Serializer,
+                            {
+                                match self {
+                                    FunctionOption::None => 0.serialize(serializer),
+                                    FunctionOption::Function(ty) => ty.serialize(serializer),
+                                }
+                            }
+                        }
+                        match &item.search_type {
+                            Some(ty) => FunctionOption::Function(ty),
+                            None => FunctionOption::None,
+                        }
+                    })
+                    .collect::<Vec<_>>(),
             )?;
             crate_data.serialize_field(
                 "p",
diff --git a/src/librustdoc/html/static/js/externs.js b/src/librustdoc/html/static/js/externs.js
index 23947d002ab..ecbe15a59da 100644
--- a/src/librustdoc/html/static/js/externs.js
+++ b/src/librustdoc/html/static/js/externs.js
@@ -86,6 +86,9 @@ let Results;
  * A pair of [inputs, outputs], or 0 for null. This is stored in the search index.
  * The JavaScript deserializes this into FunctionSearchType.
  *
+ * Numeric IDs are *ONE-indexed* into the paths array (`p`). Zero is used as a sentinel for `null`
+ * because `null` is four bytes while `0` is one byte.
+ *
  * An input or output can be encoded as just a number if there is only one of them, AND
  * it has no generics. The no generics rule exists to avoid ambiguity: imagine if you had
  * a function with a single output, and that output had a single generic:
@@ -114,6 +117,9 @@ let RawFunctionSearchType;
  * A single function input or output type. This is either a single path ID, or a pair of
  * [path ID, generics].
  *
+ * Numeric IDs are *ONE-indexed* into the paths array (`p`). Zero is used as a sentinel for `null`
+ * because `null` is four bytes while `0` is one byte.
+ *
  * @typedef {number | [number, Array<RawFunctionType>]}
  */
 let RawFunctionType;
diff --git a/src/librustdoc/html/static/js/search.js b/src/librustdoc/html/static/js/search.js
index 46fab7ee57b..75c7bd45a29 100644
--- a/src/librustdoc/html/static/js/search.js
+++ b/src/librustdoc/html/static/js/search.js
@@ -1846,9 +1846,6 @@ function initSearch(rawSearchIndex) {
     function buildItemSearchTypeAll(types, lowercasePaths) {
         const PATH_INDEX_DATA = 0;
         const GENERICS_DATA = 1;
-        if (types === null) {
-            return [];
-        }
         return types.map(type => {
             let pathIndex, generics;
             if (typeof type === "number") {
@@ -1859,6 +1856,7 @@ function initSearch(rawSearchIndex) {
                 generics = buildItemSearchTypeAll(type[GENERICS_DATA], lowercasePaths);
             }
             return {
+                // `0` is used as a sentinel because it's fewer bytes than `null`
                 name: pathIndex === 0 ? null : lowercasePaths[pathIndex - 1].name,
                 ty: pathIndex === 0 ? null : lowercasePaths[pathIndex - 1].ty,
                 generics: generics,
@@ -1884,7 +1882,8 @@ function initSearch(rawSearchIndex) {
     function buildFunctionSearchType(functionSearchType, lowercasePaths) {
         const INPUTS_DATA = 0;
         const OUTPUT_DATA = 1;
-        if (functionSearchType === 0 || functionSearchType === null) {
+        // `0` is used as a sentinel because it's fewer bytes than `null`
+        if (functionSearchType === 0) {
             return null;
         }
         let inputs, output;