diff --git a/terminaldisplay.cpp b/terminaldisplay.cpp
index f51bc19..ccdee90 100644
--- a/terminaldisplay.cpp
+++ b/terminaldisplay.cpp
@@ -73,7 +73,9 @@ std::string Display::new_frame( Framebuffer &f )
 	 && (!f.get_row( frame.y )->wrap)
 	 && (!initialized || last_frame.get_row( frame.y )->wrap) ) {
       frame.x = last_x;
-      last_frame.reset_cell( last_frame.get_cell( frame.y, frame.x ) );
+      if ( initialized ) {
+	last_frame.reset_cell( last_frame.get_cell( frame.y, frame.x ) );
+      }
 
       snprintf( tmp, 64, "\033[%d;%dH\033[K", frame.y + 1, frame.x + 1 );
       frame.append( tmp );
@@ -115,10 +117,9 @@ void Display::put_cell( FrameState &frame, Framebuffer &f )
   char tmp[ 64 ];
 
   Cell *cell = f.get_cell( frame.y, frame.x );
-  Cell *last_cell = last_frame.get_cell( frame.y, frame.x );
 
   if ( initialized
-       && ( *cell == *last_cell ) ) {
+       && ( *cell == *(last_frame.get_cell( frame.y, frame.x )) ) ) {
     frame.x += cell->width;
     return;
   }
diff --git a/terminalframebuffer.hpp b/terminalframebuffer.hpp
index b94c322..2da879e 100644
--- a/terminalframebuffer.hpp
+++ b/terminalframebuffer.hpp
@@ -5,6 +5,7 @@
 #include <deque>
 #include <string>
 #include <list>
+#include <assert.h>
 
 /* Terminal framebuffer */
 
@@ -171,6 +172,13 @@ namespace Terminal {
 
     inline Cell *get_cell( void )
     {
+#ifdef DEBUG
+      assert( ds.get_cursor_row() >= 0 );
+      assert( ds.get_cursor_col() >= 0 );
+      assert( ds.get_cursor_row() < ds.get_height() );
+      assert( ds.get_cursor_col() < ds.get_width() );
+#endif
+
       return &rows[ ds.get_cursor_row() ].cells[ ds.get_cursor_col() ];
     }
 
@@ -179,6 +187,13 @@ namespace Terminal {
       if ( row == -1 ) row = ds.get_cursor_row();
       if ( col == -1 ) col = ds.get_cursor_col();
 
+#ifdef DEBUG
+      assert( row >= 0 );
+      assert( col >= 0 );
+      assert( row < ds.get_height() );
+      assert( col < ds.get_width() );
+#endif
+
       return &rows[ row ].cells[ col ];
     }