diff --git a/Understanding-and-debugging-Nimbus-EVM-JSON-tests.md b/Understanding-and-debugging-Nimbus-EVM-JSON-tests.md
index 46e097b..ae67aba 100644
--- a/Understanding-and-debugging-Nimbus-EVM-JSON-tests.md
+++ b/Understanding-and-debugging-Nimbus-EVM-JSON-tests.md
@@ -46,6 +46,10 @@ Addition input path prefix are:
 * TransitionTests
 * ValidBlocks
 
+## Legacy tests
+
+Both General State Tests and Block Chain Tests contains legacy test suite and new test suite. If you want to select legacy test suite, please use `--legacy:true`. Default configuration will new test suite. Legacy test suite contains test data for Frontier up to Constantinople. New test suite contains test data for Istanbul onward.
+
 ## VMTests
 
 ### JSON structure