diff --git a/src/char_model_trainer.cc b/src/char_model_trainer.cc
index be0f0582..b758a8c0 100644
--- a/src/char_model_trainer.cc
+++ b/src/char_model_trainer.cc
@@ -37,7 +37,7 @@ util::Status Trainer::Train() {
     sum += it.second;
   }
 
-  const float logsum = log(sum);
+  const auto logsum = std::log(static_cast<float>(sum));
 
   CHECK_OR_RETURN(final_pieces_.empty());
   for (const auto &it : Sorted(required_chars_)) {
@@ -46,7 +46,7 @@ util::Status Trainer::Train() {
       break;
     }
     final_pieces_.emplace_back(string_util::UnicodeCharToUTF8(it.first),
-                               log(it.second) - logsum);
+                               std::log(static_cast<float>(it.second)) - logsum);
   }
 
   if (trainer_spec_.use_all_vocab()) {
diff --git a/src/unigram_model_trainer.cc b/src/unigram_model_trainer.cc
index 86c75574..5f26771a 100644
--- a/src/unigram_model_trainer.cc
+++ b/src/unigram_model_trainer.cc
@@ -43,7 +43,7 @@ double Digamma(double x) {
   const double xx = 1.0 / x;
   const double xx2 = xx * xx;
   const double xx4 = xx2 * xx2;
-  result += log(x) + (1.0 / 24.0) * xx2 - (7.0 / 960.0) * xx4 +
+  result += std::log(x) + (1.0 / 24.0) * xx2 - (7.0 / 960.0) * xx4 +
             (31.0 / 8064.0) * xx4 * xx2 - (127.0 / 30720.0) * xx4 * xx4;
   return result;
 }
diff --git a/src/word_model_trainer.cc b/src/word_model_trainer.cc
index 8d759e40..ae274d98 100644
--- a/src/word_model_trainer.cc
+++ b/src/word_model_trainer.cc
@@ -47,7 +47,7 @@ util::Status Trainer::Train() {
     sum += it.second;
   }
 
-  const float logsum = log(sum);
+  const auto logsum = std::log(static_cast<float>(sum));
 
   CHECK_OR_RETURN(final_pieces_.empty());
   for (const auto &it : Sorted(freq)) {
@@ -58,7 +58,7 @@ util::Status Trainer::Train() {
         final_pieces_.size() == static_cast<size_t>(vocab_size)) {
       break;
     }
-    final_pieces_.emplace_back(it.first, log(it.second) - logsum);
+    final_pieces_.emplace_back(it.first, std::log(static_cast<float>(it.second)) - logsum);
   }
 
   if (trainer_spec_.use_all_vocab()) {