diff --git a/src/ccutil/indexmapbidi.cpp b/src/ccutil/indexmapbidi.cpp
index baf3a4475..8460ff6be 100644
--- a/src/ccutil/indexmapbidi.cpp
+++ b/src/ccutil/indexmapbidi.cpp
@@ -123,7 +123,7 @@ void IndexMapBiDi::Setup() {
   }
   compact_map_.clear();
   compact_map_.resize(compact_size, -1);
-  for (int i = 0; i < sparse_map_.size(); ++i) {
+  for (size_t i = 0; i < sparse_map_.size(); ++i) {
     if (sparse_map_[i] >= 0) {
       compact_map_[sparse_map_[i]] = i;
     }
@@ -187,7 +187,7 @@ void IndexMapBiDi::CompleteMerges() {
   // Re-generate the compact_map leaving holes for unused indices.
   compact_map_.clear();
   compact_map_.resize(compact_size, -1);
-  for (int i = 0; i < sparse_map_.size(); ++i) {
+  for (size_t i = 0; i < sparse_map_.size(); ++i) {
     if (sparse_map_[i] >= 0) {
       if (compact_map_[sparse_map_[i]] == -1) {
         compact_map_[sparse_map_[i]] = i;
@@ -198,7 +198,7 @@ void IndexMapBiDi::CompleteMerges() {
   // index went to in the compacted map.
   std::vector<int32_t> tmp_compact_map(compact_size, -1);
   compact_size = 0;
-  for (int i = 0; i < compact_map_.size(); ++i) {
+  for (size_t i = 0; i < compact_map_.size(); ++i) {
     if (compact_map_[i] >= 0) {
       tmp_compact_map[i] = compact_size;
       compact_map_[compact_size++] = compact_map_[i];
@@ -222,7 +222,7 @@ bool IndexMapBiDi::Serialize(FILE *fp) const {
   // then each additional sparse entry needs to be stored.
   // Normally we store only the compact map to save space.
   std::vector<int32_t> remaining_pairs;
-  for (int i = 0; i < sparse_map_.size(); ++i) {
+  for (size_t i = 0; i < sparse_map_.size(); ++i) {
     if (sparse_map_[i] >= 0 && compact_map_[sparse_map_[i]] != i) {
       remaining_pairs.push_back(i);
       remaining_pairs.push_back(sparse_map_[i]);
@@ -243,10 +243,10 @@ bool IndexMapBiDi::DeSerialize(bool swap, FILE *fp) {
   }
   sparse_map_.clear();
   sparse_map_.resize(sparse_size_, -1);
-  for (int i = 0; i < compact_map_.size(); ++i) {
+  for (size_t i = 0; i < compact_map_.size(); ++i) {
     sparse_map_[compact_map_[i]] = i;
   }
-  for (int i = 0; i < remaining_pairs.size(); ++i) {
+  for (size_t i = 0; i < remaining_pairs.size(); ++i) {
     int sparse_index = remaining_pairs[i++];
     sparse_map_[sparse_index] = remaining_pairs[i];
   }
diff --git a/src/ccutil/unicharcompress.cpp b/src/ccutil/unicharcompress.cpp
index 9cb1e48e7..2c0ad5079 100644
--- a/src/ccutil/unicharcompress.cpp
+++ b/src/ccutil/unicharcompress.cpp
@@ -78,7 +78,7 @@ static bool DecodeRadicalLine(std::string &radical_data_line, RSMap *radical_map
 // is unlikely to want to use it again.
 static bool DecodeRadicalTable(std::string &radical_data, RSMap *radical_map) {
   std::vector<std::string> lines = split(radical_data, '\n');
-  for (int i = 0; i < lines.size(); ++i) {
+  for (unsigned i = 0; i < lines.size(); ++i) {
     if (!DecodeRadicalLine(lines[i], radical_map)) {
       tprintf("Invalid format in radical table at line %d: %s\n", i, lines[i].c_str());
       return false;
@@ -265,7 +265,7 @@ void UnicharCompress::DefragmentCodeValues(int encoded_null) {
   }
   // Compute offsets based on code use.
   int offset = 0;
-  for (int i = 0; i < offsets.size(); ++i) {
+  for (unsigned i = 0; i < offsets.size(); ++i) {
     // If not used, decrement everything above here.
     // We are moving encoded_null to the end, so it is not "used".
     if (offsets[i] == 0 || i == encoded_null) {
@@ -338,7 +338,7 @@ bool UnicharCompress::DeSerialize(TFile *fp) {
 // See the class comment above for details.
 std::string UnicharCompress::GetEncodingAsString(const UNICHARSET &unicharset) const {
   std::string encoding;
-  for (int c = 0; c < encoder_.size(); ++c) {
+  for (unsigned c = 0; c < encoder_.size(); ++c) {
     const RecodedCharID &code = encoder_[c];
     if (0 < c && c < SPECIAL_UNICHAR_CODES_COUNT && code == encoder_[c - 1]) {
       // Don't show the duplicate entry.
diff --git a/src/ccutil/unicharset.cpp b/src/ccutil/unicharset.cpp
index 0aa313224..cf64b18c6 100644
--- a/src/ccutil/unicharset.cpp
+++ b/src/ccutil/unicharset.cpp
@@ -883,7 +883,7 @@ void UNICHARSET::post_load_setup() {
   int x_height_alphas = 0;
   int cap_height_alphas = 0;
   top_bottom_set_ = false;
-  for (UNICHAR_ID id = 0; id < unichars.size(); ++id) {
+  for (unsigned id = 0; id < unichars.size(); ++id) {
     int min_bottom = 0;
     int max_bottom = UINT8_MAX;
     int min_top = 0;
@@ -1012,7 +1012,7 @@ bool UNICHARSET::AnyRepeatedUnicodes() const {
   if (has_special_codes()) {
     start_id = SPECIAL_UNICHAR_CODES_COUNT;
   }
-  for (int id = start_id; id < unichars.size(); ++id) {
+  for (unsigned id = start_id; id < unichars.size(); ++id) {
     // Convert to unicodes.
     std::vector<char32> unicodes = UNICHAR::UTF8ToUTF32(get_normed_unichar(id));
     for (size_t u = 1; u < unicodes.size(); ++u) {