diff --git a/src/tree/tree_model.cc b/src/tree/tree_model.cc
index 1c8ad0d9e756..a351a8f8be08 100644
--- a/src/tree/tree_model.cc
+++ b/src/tree/tree_model.cc
@@ -402,7 +402,7 @@ class JsonGenerator : public TreeGenerator {
     auto cats = GetSplitCategory(tree, nid);
     static std::string const kCategoryTemplate =
         R"I( "nodeid": {nid}, "depth": {depth}, "split": "{fname}", )I"
-        R"I("split_condition": {cond}, "yes", {right}, "no", {left}, )I"
+        R"I("split_condition": {cond}, "yes": {right}, "no": {left}, )I"
         R"I("missing", {missing})I";
     std::string cats_ptr = "[";
     for (size_t i = 0; i < cats.size(); ++i) {
diff --git a/tests/cpp/tree/test_tree_model.cc b/tests/cpp/tree/test_tree_model.cc
index 6bfecfd81149..1bda60241f65 100644
--- a/tests/cpp/tree/test_tree_model.cc
+++ b/tests/cpp/tree/test_tree_model.cc
@@ -294,6 +294,11 @@ void TestCategoricalTreeDump(std::string format, std::string sep) {
   ASSERT_NE(pos, std::string::npos);
   pos = str.find(cond_str, pos + 1);
   ASSERT_NE(pos, std::string::npos);
+
+  if (format == "json") {
+    // Make sure it's valid JSON
+    Json::Load(StringView{str});
+  }
 }
 }  // anonymous namespace