diff --git a/core/forkid/forkid.go b/core/forkid/forkid.go
index 00e2eaa34e..e655b88e60 100644
--- a/core/forkid/forkid.go
+++ b/core/forkid/forkid.go
@@ -292,6 +292,7 @@ func gatherForks(config *params.ChainConfig, genesis uint64) ([]uint64, []uint64
 	if len(forksByTime) > 0 && forksByTime[0] == 0 {
 		forksByTime = forksByTime[1:]
 	}
+	// Skip any forks by time that are non-zero, but before genesis.
 	if len(forksByTime) > 0 && forksByTime[0] <= genesis {
 		forksByTime = forksByTime[1:]
 	}