diff --git a/src/search.cpp b/src/search.cpp
index c85cdb5d..7b43f64a 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1400,7 +1400,7 @@ moves_loop: // When in check and at SpNode search starts from here
     assert(is_ok(first));
     assert(is_ok(second));
     assert(color_of(pos.piece_on(from_sq(second))) == ~pos.side_to_move());
-    assert(color_of(pos.piece_on(to_sq(first))) == ~pos.side_to_move());
+    assert(type_of(first) == CASTLE || color_of(pos.piece_on(to_sq(first))) == ~pos.side_to_move());
 
     Square m1from = from_sq(first);
     Square m2from = from_sq(second);