diff --git a/src/cryptonote_core/hardfork.cpp b/src/cryptonote_core/hardfork.cpp
index d2e95b58e..f4df1f9c6 100644
--- a/src/cryptonote_core/hardfork.cpp
+++ b/src/cryptonote_core/hardfork.cpp
@@ -43,6 +43,10 @@ HardFork::HardFork(cryptonote::BlockchainDB &db, uint8_t original_version, time_
   window_size(window_size),
   threshold_percent(threshold_percent)
 {
+  if (window_size == 0)
+    throw "window_size needs to be strictly positive";
+  if (threshold_percent > 100)
+    throw "threshold_percent needs to be between 0 and 100";
 }
 
 bool HardFork::add(uint8_t version, uint64_t height, time_t time)
@@ -93,6 +97,8 @@ bool HardFork::add(const cryptonote::block &block, uint64_t height)
   if (!do_check(block))
     return false;
 
+  db.set_hard_fork_version(height, heights[current_fork_index].version);
+
   const uint8_t version = get_effective_version(block);
 
   while (versions.size() >= window_size) {
@@ -105,16 +111,15 @@ bool HardFork::add(const cryptonote::block &block, uint64_t height)
   last_versions[version]++;
   versions.push_back(version);
 
-  uint8_t voted = get_voted_fork_index(height);
+  uint8_t voted = get_voted_fork_index(height + 1);
   if (voted > current_fork_index) {
     for (int v = heights[current_fork_index].version + 1; v <= heights[voted].version; ++v) {
-      db.set_hard_fork_starting_height(v, height);
+      // we reached the vote threshold with this block, next one will be forked
+      db.set_hard_fork_starting_height(v, height + 1);
     }
     current_fork_index = voted;
   }
 
-  db.set_hard_fork_version(height, heights[current_fork_index].version);
-
   return true;
 }
 
@@ -159,7 +164,7 @@ bool HardFork::reorganize_from_block_height(uint64_t height)
 
   for (size_t n = 0; n < 256; ++n)
     last_versions[n] = 0;
-  const uint64_t rescan_height = height >= (window_size - 1) ? height - (window_size - 1) : 0;
+  const uint64_t rescan_height = height >= (window_size - 1) ? height - (window_size  -1) : 0;
   const uint8_t start_version = height == 0 ? original_version : db.get_hard_fork_version(height);
   while (heights[current_fork_index].version > start_version) {
     db.set_hard_fork_starting_height(heights[current_fork_index].version, std::numeric_limits<uint64_t>::max());
@@ -171,6 +176,16 @@ bool HardFork::reorganize_from_block_height(uint64_t height)
     last_versions[v]++;
     versions.push_back(v);
   }
+
+  uint8_t voted = get_voted_fork_index(height + 1);
+  if (voted > current_fork_index) {
+    for (int v = heights[current_fork_index].version + 1; v <= heights[voted].version; ++v) {
+      // we reached the vote threshold with this block, next one will be forked
+      db.set_hard_fork_starting_height(v, height + 1);
+    }
+    current_fork_index = voted;
+  }
+
   const uint64_t bc_height = db.height();
   for (uint64_t h = height + 1; h < bc_height; ++h) {
     add(db.get_block_from_height(h), h);
diff --git a/tests/unit_tests/hardfork.cpp b/tests/unit_tests/hardfork.cpp
index ad00ed60f..a476eca22 100644
--- a/tests/unit_tests/hardfork.cpp
+++ b/tests/unit_tests/hardfork.cpp
@@ -238,7 +238,7 @@ TEST(steps_1, Success)
   }
 
   for (uint64_t h = 0; h < 10; ++h) {
-    ASSERT_EQ(hf.get(h), h+1);
+    ASSERT_EQ(hf.get(h), std::max(1,(int)h));
   }
 }
 
@@ -265,7 +265,7 @@ TEST(reorganize, Same)
     for (uint64_t rh = 0; rh < 20; ++rh) {
       hf.reorganize_from_block_height(rh);
       for (int hh = 0; hh < 20; ++hh) {
-        uint8_t version = hh >= (history-1) ? block_versions[hh - (history-1)] : 1;
+        uint8_t version = hh >= history ? block_versions[hh - history] : 1;
         ASSERT_EQ(hf.get(hh), version);
       }
     }
@@ -285,8 +285,10 @@ TEST(reorganize, Changed)
   ASSERT_TRUE(hf.add(9, 6, 3));
   hf.init();
 
+  //                                 fork         4     7     9
   //                                 index  0  1  2  3  4  5  6  7  8  9
   static const uint8_t block_versions[] = { 1, 1, 4, 4, 7, 7, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9 };
+  static const uint8_t expected_versions[] = { 1, 1, 1, 1, 1, 1, 4, 4, 7, 7, 9, 9, 9, 9, 9, 9 };
   for (uint64_t h = 0; h < 16; ++h) {
     db.add_block(mkblock(block_versions[h]), 0, 0, 0, crypto::hash());
     ASSERT_TRUE (hf.add(db.get_block_from_height(h), h));
@@ -295,14 +297,13 @@ TEST(reorganize, Changed)
   for (uint64_t rh = 0; rh < 16; ++rh) {
     hf.reorganize_from_block_height(rh);
     for (int hh = 0; hh < 16; ++hh) {
-      uint8_t version = hh >= (history-1) ? block_versions[hh - (history-1)] : 1;
-      ASSERT_EQ(hf.get(hh), version);
+      ASSERT_EQ(hf.get(hh), expected_versions[hh]);
     }
   }
 
   // delay a bit for 9, and go back to 1 to check it stays at 9
   static const uint8_t block_versions_new[] =    { 1, 1, 4, 4, 7, 7, 4, 7, 7, 7, 9, 9, 9, 9, 9, 1 };
-  static const uint8_t expected_versions_new[] = { 1, 1, 1, 1, 1, 4, 4, 4, 4, 4, 7, 7, 7, 9, 9, 9 };
+  static const uint8_t expected_versions_new[] = { 1, 1, 1, 1, 1, 1, 4, 4, 4, 4, 4, 7, 7, 7, 9, 9 };
   for (uint64_t h = 3; h < 16; ++h) {
     db.remove_block();
   }
@@ -336,11 +337,13 @@ TEST(voting, threshold)
       db.add_block(mkblock(v), 0, 0, 0, crypto::hash());
       bool ret = hf.add(db.get_block_from_height(h), h);
       if (h >= 8 && threshold == 87) {
+        // for threshold 87, we reach the treshold at height 7, so from height 8, hard fork to version 2, but 8 tries to add 1
         ASSERT_FALSE(ret);
       }
       else {
+        // for threshold 88, we never reach the threshold
         ASSERT_TRUE(ret);
-        uint8_t expected = threshold == 88 ? 1 : h < 7 ? 1 : 2;
+        uint8_t expected = threshold == 88 ? 1 : h < 8 ? 1 : 2;
         ASSERT_EQ(hf.get(h), expected);
       }
     }
@@ -370,7 +373,7 @@ TEST(new_blocks, denied)
     ASSERT_FALSE(hf.add(mkblock(1), 9)); // so this one can't get added
     ASSERT_TRUE(hf.add(mkblock(2), 10));
 
-    ASSERT_EQ(hf.get_start_height(2), 8);
+    ASSERT_EQ(hf.get_start_height(2), 9);
 }
 
 TEST(new_version, early)
@@ -428,8 +431,8 @@ TEST(reorganize, changed)
     ADD_TRUE(3, 7);
     ADD_TRUE(4, 8);
     ADD_TRUE(4, 9);
-    ASSERT_EQ(hf.get_start_height(2), 3);
-    ASSERT_EQ(hf.get_start_height(3), 8);
+    ASSERT_EQ(hf.get_start_height(2), 4); // reaches threshold 2 at height 3, so height 4 forks
+    ASSERT_EQ(hf.get_start_height(3), 9);
     ASSERT_EQ(hf.get_current_version(), 3);
 
     // pop a few blocks and check current version goes back down
@@ -446,7 +449,7 @@ TEST(reorganize, changed)
     ADD_TRUE(2, 7);
     ADD_TRUE(2, 8);
     ADD_TRUE(2, 9);
-    ASSERT_EQ(hf.get_start_height(2), 3); // unchanged
+    ASSERT_EQ(hf.get_start_height(2), 4); // unchanged
     ASSERT_EQ(hf.get_current_version(), 2); // we did not bump to 3 this time
     ASSERT_EQ(hf.get_start_height(3), std::numeric_limits<uint64_t>::max()); // not yet
 }