diff --git a/src/dispnew.c b/src/dispnew.c
index f96db302781..f834f359ec5 100644
--- a/src/dispnew.c
+++ b/src/dispnew.c
@@ -683,7 +683,9 @@ void
 clear_glyph_matrix_rows (struct glyph_matrix *matrix, int start, int end)
 {
   eassert (start <= end);
-  eassert (start >= 0 && start <= matrix->nrows);
+  eassert (start >= 0 && (start < matrix->nrows
+			  /* matrix->nrows can be 0 for the initial frame.  */
+			  || (matrix->nrows == 0)));
   eassert (end >= 0 && end <= matrix->nrows);
 
   for (; start < end; ++start)