diff --git a/BasiliskII/src/Unix/video_vosf.h b/BasiliskII/src/Unix/video_vosf.h
index dae9c8b5..fd3d43da 100644
--- a/BasiliskII/src/Unix/video_vosf.h
+++ b/BasiliskII/src/Unix/video_vosf.h
@@ -350,6 +350,39 @@ static bool Screen_fault_handler_init()
  *	Update display for Windowed mode and VOSF
  */
 
+/*	How can we deal with array overrun conditions ?
+	
+	The state of the framebuffer pages that have been touched are maintained
+	in the dirtyPages[] table. That table is (pageCount + 2) bytes long.
+
+Terminology
+	
+	"Last Page" denotes the pageCount-nth page, i.e. dirtyPages[pageCount - 1].
+	"CLEAR Page Guard" refers to the page following the Last Page but is always
+	in the CLEAR state. "SET Page Guard" refers to the page following the CLEAR
+	Page Guard but is always in the SET state.
+
+Rough process
+	
+	The update routines must determine which pages have to blitted to the
+	screen. This job consists in finding the first_page that was touched.
+	i.e. find the next page that is SET. Then, finding how many pages were
+	touched starting from first_page. i.e. find the next page that is CLEAR.
+
+Two cases
+
+	- Last Page is CLEAR: find_next_page_set() will reach the SET Page Guard
+	but it is beyond the valid pageCount value. Therefore, we exit from the
+	update routine.
+	
+	- Last Page is SET: first_page equals (pageCount - 1) and
+	find_next_page_clear() will reach the CLEAR Page Guard. We blit the last
+	page to the screen. On the next iteration, page equals pageCount and
+	find_next_page_set() will reach the SET Page Guard. We still safely exit
+	from the update routine because the SET Page Guard position is greater
+	than pageCount.
+*/
+
 static inline void update_display_window_vosf(void)
 {
 	int page = 0;
diff --git a/BasiliskII/src/Unix/video_x.cpp b/BasiliskII/src/Unix/video_x.cpp
index 886f8aa3..55802a1f 100644
--- a/BasiliskII/src/Unix/video_x.cpp
+++ b/BasiliskII/src/Unix/video_x.cpp
@@ -264,8 +264,6 @@ static inline int find_next_page_clear(int page)
 	char *match = strchr(mainBuffer.dirtyPages + page, PFLAG_CLEAR_VALUE);
 	return match ? match - mainBuffer.dirtyPages : mainBuffer.pageCount;
 #else
-	// NOTE: the loop is bound to terminate because the last
-	// page in mainBuffer.dirtyPages[] shall be set to CLEAR
 	while (PFLAG_ISSET_4(page))
 		page += 4;
 	while (PFLAG_ISSET(page))
@@ -945,7 +943,7 @@ bool VideoInitBuffer()
 		if (mainBuffer.dirtyPages != 0)
 			free(mainBuffer.dirtyPages);
 
-		mainBuffer.dirtyPages = (char *) malloc(mainBuffer.pageCount + 1);
+		mainBuffer.dirtyPages = (char *) malloc(mainBuffer.pageCount + 2);
 
 		if (mainBuffer.pageInfo != 0)
 			free(mainBuffer.pageInfo);
@@ -956,12 +954,10 @@ bool VideoInitBuffer()
 			return false;
 
 		PFLAG_CLEAR_ALL;
-		
-		// Make sure there is at least one page marked, so the
-		// loops in the update routine will terminate
-		// gb-- Set the last page as cleared because the update
-		// routine finally searches for a page that was not touched
+		// Safety net to insure the loops in the update routines will terminate
+		// See a discussion in <video_vosf.h> for further details
 		PFLAG_CLEAR(mainBuffer.pageCount);
+		PFLAG_SET(mainBuffer.pageCount+1);
 
 		uint32 a = 0;
 		for (int i = 0; i < mainBuffer.pageCount; i++) {
@@ -1955,7 +1951,7 @@ static void update_display_static(void)
 
 // We suggest the compiler to inline the next two functions so that it
 // may specialise the code according to the current screen depth and
-// display type. A clever compiler would that job by itself though...
+// display type. A clever compiler would do that job by itself though...
 
 // NOTE: update_display_vosf is inlined too