diff --git a/src/io/tree.cpp b/src/io/tree.cpp
index 6cd0d50b4da7..39b5c23d4d1c 100644
--- a/src/io/tree.cpp
+++ b/src/io/tree.cpp
@@ -523,35 +523,32 @@ std::string Tree::NumericalDecisionIfElse(int node) const {
   str_buf << std::setprecision(std::numeric_limits<double>::digits10 + 2);
   uint8_t missing_type = GetMissingType(decision_type_[node]);
   bool default_left = GetDecisionType(decision_type_[node], kDefaultLeftMask);
-  if (missing_type == MissingType::None
-      || (missing_type == MissingType::Zero && default_left && kZeroThreshold < threshold_[node])) {
-    str_buf << "if (fval <= " << threshold_[node] << ") {";
-  } else if (missing_type == MissingType::Zero) {
+  if (missing_type != MissingType::NaN) {
+    str_buf << "if (std::isnan(fval)) fval = 0.0;";
+  }
+  if (missing_type == MissingType::Zero) {
     if (default_left) {
-      str_buf << "if (fval <= " << threshold_[node] << " || Tree::IsZero(fval)" << " || std::isnan(fval)) {";
+      str_buf << "if (Tree::IsZero(fval)) {";
     } else {
-      str_buf << "if (fval <= " << threshold_[node] << " && !Tree::IsZero(fval)" << " && !std::isnan(fval)) {";
+      str_buf << "if (!Tree::IsZero(fval)) {";
     }
-  } else {
+  } else if (missing_type == MissingType::NaN) {
     if (default_left) {
-      str_buf << "if (fval <= " << threshold_[node] << " || std::isnan(fval)) {";
+      str_buf << "if (std::isnan(fval)) {";
     } else {
-      str_buf << "if (fval <= " << threshold_[node] << " && !std::isnan(fval)) {";
+      str_buf << "if (!std::isnan(fval)) {";
     }
+  } else {
+    str_buf << "if (fval <= " << threshold_[node] << ") {";
   }
   return str_buf.str();
 }
 
 std::string Tree::CategoricalDecisionIfElse(int node) const {
-  uint8_t missing_type = GetMissingType(decision_type_[node]);
   std::stringstream str_buf;
   Common::C_stringstream(str_buf);
-  if (missing_type == MissingType::NaN) {
-    str_buf << "if (std::isnan(fval)) { int_fval = -1; } else { int_fval = static_cast<int>(fval); }";
-  } else {
-    str_buf << "if (std::isnan(fval)) { int_fval = 0; } else { int_fval = static_cast<int>(fval); }";
-  }
   int cat_idx = static_cast<int>(threshold_[node]);
+  str_buf << "if (std::isnan(fval)) { int_fval = -1; } else { int_fval = static_cast<int>(fval); }";
   str_buf << "if (int_fval >= 0 && int_fval < 32 * (";
   str_buf << cat_boundaries_[cat_idx + 1] - cat_boundaries_[cat_idx];
   str_buf << ") && (((cat_threshold[" << cat_boundaries_[cat_idx];