diff --git a/src/test/skiplist_tests.cpp b/src/test/skiplist_tests.cpp
--- a/src/test/skiplist_tests.cpp
+++ b/src/test/skiplist_tests.cpp
@@ -48,7 +48,7 @@
     // Build a main chain 100000 blocks long.
     std::vector<uint256> vHashMain(100000);
     std::vector<CBlockIndex> vBlocksMain(100000);
-    for (unsigned int i = 0; i < vBlocksMain.size(); i++) {
+    for (size_t i = 0; i < vBlocksMain.size(); i++) {
         // Set the hash equal to the height, so we can quickly check the
         // distances.
         vHashMain[i] = ArithToUint256(i);
@@ -67,7 +67,7 @@
     // Build a branch that splits off at block 49999, 50000 blocks long.
     std::vector<uint256> vHashSide(50000);
     std::vector<CBlockIndex> vBlocksSide(50000);
-    for (unsigned int i = 0; i < vBlocksSide.size(); i++) {
+    for (size_t i = 0; i < vBlocksSide.size(); i++) {
         // Add 1<<128 to the hashes, so GetLow64() still returns the height.
         vHashSide[i] = ArithToUint256(i + 50000 + (arith_uint256(1) << 128));
         vBlocksSide[i].nHeight = i + 50000;
@@ -108,7 +108,7 @@
         // The further ones (excluding the last one) go back with exponential
         // steps.
         unsigned int dist = 2;
-        for (unsigned int i = 12; i < locator.vHave.size() - 1; i++) {
+        for (size_t i = 12; i < locator.vHave.size() - 1; i++) {
             BOOST_CHECK_EQUAL(UintToArith256(locator.vHave[i - 1]).GetLow64() -
                                   UintToArith256(locator.vHave[i]).GetLow64(),
                               dist);
@@ -120,7 +120,7 @@
 BOOST_AUTO_TEST_CASE(findearliestatleast_test) {
     std::vector<uint256> vHashMain(100000);
     std::vector<CBlockIndex> vBlocksMain(100000);
-    for (unsigned int i = 0; i < vBlocksMain.size(); i++) {
+    for (size_t i = 0; i < vBlocksMain.size(); i++) {
         // Set the hash equal to the height
         vHashMain[i] = ArithToUint256(i);
         vBlocksMain[i].nHeight = i;
@@ -141,7 +141,7 @@
     }
     // Check that we set nTimeMax up correctly.
     unsigned int curTimeMax = 0;
-    for (unsigned int i = 0; i < vBlocksMain.size(); ++i) {
+    for (size_t i = 0; i < vBlocksMain.size(); ++i) {
         curTimeMax = std::max(curTimeMax, vBlocksMain[i].nTime);
         BOOST_CHECK(curTimeMax == vBlocksMain[i].nTimeMax);
     }