diff --git a/src/learn/learner.cpp b/src/learn/learner.cpp
index 4b76e444..998c82eb 100644
--- a/src/learn/learner.cpp
+++ b/src/learn/learner.cpp
@@ -639,13 +639,21 @@ void MultiThinkGenSfen::thread_worker(size_t thread_id)
 					}
 
 					// reach leaf
-					// cout << pos;
-
-					auto v = Eval::evaluate(pos);
-					// evaluate() returns the evaluation value on the turn side, so
-					// If it's a turn different from root_color, you must invert v and return it.
-					if (rootColor != pos.side_to_move())
-						v = -v;
+					Value v;
+					if (pos.checkers()) {
+						// Sometime a king is checked.  An example is a case that a checkmate is
+						// found in the search.  If Eval::evaluate() is called whne a king is
+						// checked, classic eval crashes by an assertion.  To avoid crashes, return
+						// value1 instead of the score of the PV leaf.
+						v = value1;
+					}
+					else {
+						v = Eval::evaluate(pos);
+						// evaluate() returns the evaluation value on the turn side, so
+						// If it's a turn different from root_color, you must invert v and return it.
+						if (rootColor != pos.side_to_move())
+							v = -v;
+					}
 
 					// Rewind.
 					// Is it C++x14, and isn't there even foreach to turn in reverse?