diff --git a/src/common/json.cc b/src/common/json.cc
index de9a89f78..21be2a5bc 100644
--- a/src/common/json.cc
+++ b/src/common/json.cc
@@ -791,7 +791,7 @@ Json UBJReader::Parse() {
         return Json{JsonBoolean{true}};
       }
       case 'F': {
-        return Json{JsonBoolean{true}};
+        return Json{JsonBoolean{false}};
       }
       case 'd': {
         auto v = this->ReadPrimitive<float>();
diff --git a/tests/cpp/common/test_json.cc b/tests/cpp/common/test_json.cc
index d361552ce..155cf04ad 100644
--- a/tests/cpp/common/test_json.cc
+++ b/tests/cpp/common/test_json.cc
@@ -677,6 +677,21 @@ TEST(UBJson, Basic) {
     ASSERT_FLOAT_EQ(3.14, get<Number>(get<Array>(ret["test"])[1]));
     ASSERT_FLOAT_EQ(2.71, get<Number>(get<Array>(ret["test"])[0]));
   }
+  {
+    // boolean
+    Json boolean{Object{}};
+    boolean["foo"] = Boolean{false};
+    std::vector<char> out;
+    Json::Dump(boolean, &out, std::ios::binary);
+    auto loaded = Json::Load(StringView{out.data(), out.size()}, std::ios::binary);
+
+    ASSERT_EQ(boolean, loaded);
+
+    boolean["foo"] = Boolean{true};
+    Json::Dump(boolean, &out, std::ios::binary);
+    loaded = Json::Load(StringView{out.data(), out.size()}, std::ios::binary);
+    ASSERT_EQ(boolean, loaded);
+  }
 }
 
 TEST(Json, TypeCheck) {