diff --git a/src/ccstruct/seam.cpp b/src/ccstruct/seam.cpp
index 6d7edbe0..431c0bc3 100644
--- a/src/ccstruct/seam.cpp
+++ b/src/ccstruct/seam.cpp
@@ -61,7 +61,7 @@ bool SEAM::PrepareToInsertSeam(const std::vector<SEAM *> &seams,
   if (!FindBlobWidth(blobs, insert_index, modify)) {
     return false;
   }
-  for (int s = insert_index; s < seams.size(); ++s) {
+  for (unsigned s = insert_index; s < seams.size(); ++s) {
     if (!seams[s]->FindBlobWidth(blobs, s + 1, modify)) {
       return false;
     }
@@ -81,7 +81,7 @@ bool SEAM::FindBlobWidth(const std::vector<TBLOB *> &blobs, int index, bool modi
     const SPLIT &split = splits_[s];
     bool found_split = split.ContainedByBlob(*blobs[index]);
     // Look right.
-    for (int b = index + 1; !found_split && b < blobs.size(); ++b) {
+    for (unsigned b = index + 1; !found_split && b < blobs.size(); ++b) {
       found_split = split.ContainedByBlob(*blobs[b]);
       if (found_split && b - index > widthp_ && modify) {
         widthp_ = b - index;
@@ -158,8 +158,8 @@ void SEAM::Print(const char *label) const {
 void SEAM::PrintSeams(const char *label, const std::vector<SEAM *> &seams) {
   if (!seams.empty()) {
     tprintf("%s\n", label);
-    for (int x = 0; x < seams.size(); ++x) {
-      tprintf("%2d:   ", x);
+    for (unsigned x = 0; x < seams.size(); ++x) {
+      tprintf("%2u:   ", x);
       seams[x]->Print("");
     }
     tprintf("\n");
diff --git a/unittest/lang_model_test.cc b/unittest/lang_model_test.cc
index e3c3796b..e0d96abc 100644
--- a/unittest/lang_model_test.cc
+++ b/unittest/lang_model_test.cc
@@ -101,7 +101,7 @@ TEST(LangModelTest, AddACharacter) {
   int null2 = trainer2.null_char();
   EXPECT_EQ(null1 + 1, null2);
   std::vector<int> labels1_v(labels1.size());
-  for (int i = 0; i < labels1.size(); ++i) {
+  for (unsigned i = 0; i < labels1.size(); ++i) {
     if (labels1[i] == null1) {
       labels1_v[i] = null2;
     } else {
@@ -186,7 +186,7 @@ TEST(LangModelTest, AddACharacterHindi) {
   int null2 = trainer2.null_char();
   EXPECT_EQ(null1 + 1, null2);
   std::vector<int> labels1_v(labels1.size());
-  for (int i = 0; i < labels1.size(); ++i) {
+  for (unsigned i = 0; i < labels1.size(); ++i) {
     if (labels1[i] == null1) {
       labels1_v[i] = null2;
     } else {
diff --git a/unittest/lstmtrainer_test.cc b/unittest/lstmtrainer_test.cc
index 6b9bbd7b..c9709437 100644
--- a/unittest/lstmtrainer_test.cc
+++ b/unittest/lstmtrainer_test.cc
@@ -48,7 +48,7 @@ TEST_F(LSTMTrainerTest, MapCoder) {
   std::vector<int> mapping =
       fra_trainer.MapRecoder(deu_trainer.GetUnicharset(), deu_trainer.GetRecoder());
   std::vector<int> mapped_fra_labels(fra_labels.size(), -1);
-  for (int i = 0; i < fra_labels.size(); ++i) {
+  for (unsigned i = 0; i < fra_labels.size(); ++i) {
     mapped_fra_labels[i] = mapping[fra_labels[i]];
     EXPECT_NE(-1, mapped_fra_labels[i]) << "i=" << i << ", ch=" << kTestStr[i];
     EXPECT_EQ(mapped_fra_labels[i], deu_labels[i])
diff --git a/unittest/recodebeam_test.cc b/unittest/recodebeam_test.cc
index 6027821c..cda970b4 100644
--- a/unittest/recodebeam_test.cc
+++ b/unittest/recodebeam_test.cc
@@ -126,9 +126,9 @@ protected:
     // Now decode using recoder_.
     std::string decoded;
     int end = 1;
-    for (int start = 0; start < labels.size(); start = end) {
+    for (unsigned start = 0; start < labels.size(); start = end) {
       RecodedCharID code;
-      int index = start;
+      unsigned index = start;
       int uni_id = INVALID_UNICHAR_ID;
       do {
         code.Set(code.length(), labels[index++]);
@@ -153,7 +153,7 @@ protected:
                                             &ratings, &xcoords);
     std::string u_decoded;
     float total_rating = 0.0f;
-    for (int u = 0; u < unichar_ids.size(); ++u) {
+    for (unsigned u = 0; u < unichar_ids.size(); ++u) {
       // To the extent of truth_utf8, we expect decoded to match, but if
       // transcription is shorter, that is OK too, as we may just be testing
       // that we get a valid sequence when padded with random data.
diff --git a/unittest/tablerecog_test.cc b/unittest/tablerecog_test.cc
index 2364e884..3556f9bc 100644
--- a/unittest/tablerecog_test.cc
+++ b/unittest/tablerecog_test.cc
@@ -51,14 +51,14 @@ public:
     EXPECT_EQ(3 + (almost_done - second) / add, cell_x_.size());
     EXPECT_EQ(x_min, cell_x_.at(0));
     EXPECT_EQ(x_max, cell_x_.at(cell_x_.size() - 1));
-    for (int i = 1; i < cell_x_.size() - 1; ++i) {
+    for (unsigned i = 1; i < cell_x_.size() - 1; ++i) {
       EXPECT_EQ(second + add * (i - 1), cell_x_.at(i));
     }
   }
 
   void ExpectSortedX() {
     EXPECT_GT(cell_x_.size(), 0);
-    for (int i = 1; i < cell_x_.size(); ++i) {
+    for (unsigned i = 1; i < cell_x_.size(); ++i) {
       EXPECT_LT(cell_x_.at(i - 1), cell_x_.at(i));
     }
   }
diff --git a/unittest/tfile_test.cc b/unittest/tfile_test.cc
index 162d0b46..aeb77744 100644
--- a/unittest/tfile_test.cc
+++ b/unittest/tfile_test.cc
@@ -44,11 +44,11 @@ protected:
     void ExpectEq(const MathData &other) {
       // Check the data.
       EXPECT_EQ(num_squares_, other.num_squares_);
-      for (int s = 0; s < squares_.size(); ++s) {
+      for (unsigned s = 0; s < squares_.size(); ++s) {
         EXPECT_EQ(squares_[s], other.squares_[s]);
       }
       EXPECT_EQ(num_triangles_, other.num_triangles_);
-      for (int s = 0; s < triangles_.size(); ++s) {
+      for (unsigned s = 0; s < triangles_.size(); ++s) {
         EXPECT_EQ(triangles_[s], other.triangles_[s]);
       }
     }