diff --git a/src/main/java/dotsandboxes/DotsAndBoxesGrid.java b/src/main/java/dotsandboxes/DotsAndBoxesGrid.java
index a9e7c5b6639e8a2a8728809d9b17c8d155baf9b6..8042a4912e9c00f05a0871e6afd96fe486dabac9 100644
--- a/src/main/java/dotsandboxes/DotsAndBoxesGrid.java
+++ b/src/main/java/dotsandboxes/DotsAndBoxesGrid.java
@@ -111,8 +111,7 @@ public class DotsAndBoxesGrid {
         }
 
         // A box is complete if the north and south horizontals and the east and west verticals have all been drawn.
-        // FIXME: You'll need to fix this code (after writing a test first).
-        return true;
+        return (getHorizontal(x, y) && getHorizontal(x , y + 1) && getVertical(x, y) && getVertical(x+1, y));
     }
 
     /** Tries to claim a box for a player. If the box is complete, sets the ownership and returns true. */
@@ -139,7 +138,10 @@ public class DotsAndBoxesGrid {
             throw new IndexOutOfBoundsException(String.format("y was %d, which is out of range. Range is 0 to %d", y, height));
         }
 
-        // FIXME: You need to throw an exception if the line was already drawn.
+        // throw exception if attempting to draw over a line that was previously drawn
+        if (getHorizontal(x, y)) {
+            throw new IllegalStateException("horizontal line already drawn");
+        }
 
         this.horizontals[x][y] = true;
 
@@ -170,7 +172,10 @@ public class DotsAndBoxesGrid {
             throw new IndexOutOfBoundsException(String.format("y was %d, which is out of range. Range is 0 to %d", y, height - 1));
         }
 
-        // You need to throw an exception if the line was already drawn.
+        // throw exception if attempting to draw over a line that was previously drawn
+        if (getVertical(x, y)) {
+            throw new IllegalStateException("vertical line already drawn");
+        }
 
         this.verticals[x][y] = true;
         // Try to claim the north or south boxes