diff --git a/assets/javascripts/lib/util.js b/assets/javascripts/lib/util.js
index ca977da113..555c129e33 100644
--- a/assets/javascripts/lib/util.js
+++ b/assets/javascripts/lib/util.js
@@ -450,6 +450,9 @@ $.escapeRegexp = (string) => string.replace(ESCAPE_REGEXP, "\\$1");
 
 $.urlDecode = (string) => decodeURIComponent(string.replace(/\+/g, "%20"));
 
+// Hash fragments are not form-encoded, so literal plus signs must stay plus signs.
+$.urlDecodeFragment = (string) => decodeURIComponent(string);
+
 $.classify = function (string) {
   string = string.split("_");
   for (let i = 0; i < string.length; i++) {
diff --git a/assets/javascripts/views/search/search.js b/assets/javascripts/views/search/search.js
index 163d96e1f7..94105618f0 100644
--- a/assets/javascripts/views/search/search.js
+++ b/assets/javascripts/views/search/search.js
@@ -216,7 +216,7 @@ app.views.Search = class Search extends app.View {
 
   getHashValue() {
     try {
-      return Search.HASH_RGX.exec($.urlDecode(location.hash))?.[1];
+      return Search.HASH_RGX.exec($.urlDecodeFragment(location.hash))?.[1];
     } catch (error) {}
   }
 };
diff --git a/assets/javascripts/views/search/search_scope.js b/assets/javascripts/views/search/search_scope.js
index c06d54e0ae..45984bc176 100644
--- a/assets/javascripts/views/search/search_scope.js
+++ b/assets/javascripts/views/search/search_scope.js
@@ -157,7 +157,7 @@ app.views.SearchScope = class SearchScope extends app.View {
   extractHashValue() {
     const value = this.getHashValue();
     if (value) {
-      const newHash = $.urlDecode(location.hash).replace(
+      const newHash = $.urlDecodeFragment(location.hash).replace(
         `#${SearchScope.SEARCH_PARAM}=${value} `,
         `#${SearchScope.SEARCH_PARAM}=`
       );
@@ -168,7 +168,7 @@ app.views.SearchScope = class SearchScope extends app.View {
 
   getHashValue() {
     try {
-      return SearchScope.HASH_RGX.exec($.urlDecode(location.hash))?.[1];
+      return SearchScope.HASH_RGX.exec($.urlDecodeFragment(location.hash))?.[1];
     } catch (error) {}
   }
 
diff --git a/test/assets/search_hash_test.js b/test/assets/search_hash_test.js
new file mode 100644
index 0000000000..276f3df387
--- /dev/null
+++ b/test/assets/search_hash_test.js
@@ -0,0 +1,50 @@
+const assert = require("node:assert/strict");
+const fs = require("node:fs");
+const test = require("node:test");
+const vm = require("node:vm");
+
+const context = {
+  app: {
+    config: { search_param: "q" },
+    router: { replaceHash: () => {} },
+    views: {},
+    View: class {},
+  },
+  location: { hash: "" },
+  $: {
+    urlDecodeFragment: decodeURIComponent,
+  },
+};
+
+vm.createContext(context);
+
+for (const file of [
+  "assets/javascripts/views/search/search_scope.js",
+  "assets/javascripts/views/search/search.js",
+]) {
+  vm.runInContext(fs.readFileSync(file, "utf8"), context, {
+    filename: file,
+  });
+}
+
+test("URL search hash preserves plus signs in a scoped C++ query", () => {
+  context.location.hash = "#q=c++%20std::min";
+
+  const scope = new context.app.views.SearchScope();
+  let replacedHash;
+  context.app.router.replaceHash = (hash) => {
+    replacedHash = hash;
+  };
+
+  assert.equal(scope.getHashValue(), "c++");
+  assert.equal(scope.extractHashValue(), "c++");
+  assert.equal(replacedHash, "#q=std::min");
+});
+
+test("URL search hash preserves encoded literal plus signs in the query", () => {
+  context.location.hash = "#q=operator%2B";
+
+  const search = new context.app.views.Search();
+
+  assert.equal(search.getHashValue(), "operator+");
+});