See attached patch.
>From f6c18450a99875647d85f633fef00e72a0c1577b Mon Sep 17 00:00:00 2001
From: sin <s...@2f30.org>
Date: Wed, 15 Apr 2015 09:43:06 +0100
Subject: [PATCH] Fix memmove() invocation with src/dst being NULL

This fixes a segmentation fault on some systems.
---
 st.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/st.c b/st.c
index b1d3791..bb8c365 100644
--- a/st.c
+++ b/st.c
@@ -2788,8 +2788,11 @@ tresize(int col, int row) {
                free(term.line[i]);
                free(term.alt[i]);
        }
-       memmove(term.line, term.line + i, row * sizeof(Line));
-       memmove(term.alt, term.alt + i, row * sizeof(Line));
+       /* ensure that both src and dst are not NULL */
+       if (i > 0) {
+               memmove(term.line, term.line + i, row * sizeof(Line));
+               memmove(term.alt, term.alt + i, row * sizeof(Line));
+       }
        for(i += row; i < term.row; i++) {
                free(term.line[i]);
                free(term.alt[i]);
-- 
1.8.4

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