diff --git a/tests/unit_tests/hardfork.cpp b/tests/unit_tests/hardfork.cpp
index 7b487481..be2885f4 100644
--- a/tests/unit_tests/hardfork.cpp
+++ b/tests/unit_tests/hardfork.cpp
@@ -117,7 +117,7 @@ public:
     blocks.push_back(blk);
   }
   virtual block get_block_from_height(const uint64_t& height) const {
-    return blocks[height];
+    return blocks.at(height);
   }
   virtual void set_hard_fork_version(uint64_t height, uint8_t version) {
     if (versions.size() <= height) 
@@ -125,7 +125,7 @@ public:
     versions[height] = version;
   }
   virtual uint8_t get_hard_fork_version(uint64_t height) const {
-    return versions[height];
+    return versions.at(height);
   }
   virtual void check_hard_fork_info() {}