diff --git a/game.cpp b/game.cpp
index 964f74f..215c9a2 100644
--- a/game.cpp
+++ b/game.cpp
@@ -85,6 +85,7 @@ void Game::must_be(int n, int must_col) {
 void Game::empty_color(int col) {
 	for(int n = 0; n < N; n++)
 		possible[n][col] = 0;
+	empty_colors[col] = true;
 }
 
 // Specific reactions