diff --git a/led-matrix.cc b/led-matrix.cc
index d8e223a..c962909 100644
--- a/led-matrix.cc
+++ b/led-matrix.cc
@@ -74,7 +74,7 @@ void RGBMatrix::ClearScreen() {
 
 void RGBMatrix::SetPixel(uint8_t x, uint8_t y,
                          uint8_t red, uint8_t green, uint8_t blue) {
-  if (x > 31 || y > 31) return;
+  if (x >= kColumns || y > 31) return;
   // TODO: re-map values to be luminance corrected (sometimes called 'gamma').
   // Ideally, we had like 10PWM bits for this, but we're too slow for that :/
   
diff --git a/led-matrix.h b/led-matrix.h
index a2b41e4..12d4781 100644
--- a/led-matrix.h
+++ b/led-matrix.h
@@ -1,3 +1,4 @@
+// -*- c++ -*-
 // Controlling a 32x32 RGB matrix via GPIO.
 
 #ifndef RPI_RGBMATRIX_H
@@ -18,13 +19,16 @@ class RGBMatrix {
   // thread.
   void UpdateScreen();
 
+  int columns() { return kColumns; }
+
 private:
   GPIO *const io_;
 
   enum {
+    kChainedBoards = 1,   // Number of boards that are daisy-chained.
     kRows = 16,
-    kColumns = 32,
-    kPWMBits = 7  // maximum PWM resolution.
+    kColumns = kChainedBoards * 32,
+    kPWMBits = 7     // maximum PWM resolution.
   };
 
   union IoBits {
diff --git a/main.cc b/main.cc
index e7438b4..6ba9116 100644
--- a/main.cc
+++ b/main.cc
@@ -153,16 +153,18 @@ public:
   }
 
   void Run() {
+    const int columns = matrix_->columns();
     while (running_) {
       if (image_ == NULL) {
         usleep(100 * 1000);
         continue;
       }
       usleep(30 * 1000);
-      for (int x = 0; x < 32; ++x) {
+      for (int x = 0; x < columns; ++x) {
         for (int y = 0; y < 32; ++y) {
           const Pixel &p = getPixel((horizontal_position_ + x) % width_, y);
-          int disp_x = 31 - x;  // Display upside down on my desk. Lets flip :)
+          // Display upside down on my desk. Lets flip :)
+          int disp_x = columns - x;
           int disp_y = 31 - y;
           matrix_->SetPixel(disp_x, disp_y, p.red, p.green, p.blue);
         }