1 files changed, 5 insertions, 0 deletions

diff --git a/src/dispnew.c b/src/dispnew.c
index fd467f4a6d3..b20383dcfa9 100644
--- a/src/dispnew.c
+++ b/src/dispnew.c
@@ -667,6 +667,7 @@ adjust_glyph_matrix (w, matrix, x, y, dim)
   
   /* Number of rows to be used by MATRIX.  */
   matrix->nrows = dim.height;
+  xassert (matrix->nrows >= 0);
 
   /* Mark rows in a current matrix of a window as not having valid
      contents.  It's important to not do this for desired matrices.
@@ -809,6 +810,10 @@ enable_glyph_matrix_rows (matrix, start, end, enabled_p)
      int start, end;
      int enabled_p;
 {
+  xassert (start <= end);
+  xassert (start >= 0 && start < matrix->nrows);
+  xassert (end >= 0 && end <= matrix->nrows);
+  
   for (; start < end; ++start)
     matrix->rows[start].enabled_p = enabled_p != 0;
 }