diff -r 4d030da07c88 -r 3ab0c2e1a4e2 src/chess/rules.c
--- a/src/chess/rules.c	Tue Apr 01 10:28:08 2014 +0200
+++ b/src/chess/rules.c	Tue Apr 01 12:30:25 2014 +0200
@@ -90,6 +90,30 @@
     }
 }
 
+_Bool is_covered(GameState *gamestate,uint8_t row,uint8_t file,uint8_t color) {
+    Move threats[16];
+    int threatcount = 0;
+    for (uint8_t r = 0 ; r < 8 ; r++) {
+        for (uint8_t f = 0 ; f < 8 ; f++) {
+            if ((gamestate->board[r][f] & COLOR_MASK) == color) {
+                threats[threatcount].piece = gamestate->board[r][f];
+                threats[threatcount].fromrow = r;
+                threats[threatcount].fromfile = f;
+                threats[threatcount].torow = row;
+                threats[threatcount].tofile = file;
+                threatcount++;
+            }
+        }
+    }
+    
+    for (int i = 0 ; i < threatcount ; i++) {
+        if (validate_move(gamestate, &(threats[i]))) {
+            return 1;
+        }
+    }
+    
+    return 0;
+}
 
 void apply_move(GameState *gamestate, Move *move) {
     uint8_t piece = move->piece & PIECE_MASK;
@@ -190,10 +214,15 @@
         result = 0;
     }
     
+    /* cancel processing to avoid recursion overflow with is_covered() */
+    if (!result) {
+        return 0;
+    }
+    
     /* is piece pinned */
     // TODO: make it so
     
-    /* correct check and checkmate flags */
+    /* correct check and checkmate flags (move is still valid) */
     // TODO: make it so
     
     return result;