diff --git a/src/regexp_bt.c b/src/regexp_bt.c
index 4082f59..793faaf 100644
--- a/src/regexp_bt.c
+++ b/src/regexp_bt.c
@@ -3360,8 +3360,17 @@
 		int	mark = OPERAND(scan)[0];
 		int	cmp = OPERAND(scan)[1];
 		pos_T	*pos;
+		size_t	col = REG_MULTI ? rex.input - rex.line : 0;
 
 		pos = getmark_buf(rex.reg_buf, mark, FALSE);
+
+		// Line may have been freed, get it again.
+		if (REG_MULTI)
+		{
+		    rex.line = reg_getline(rex.lnum);
+		    rex.input = rex.line + col;
+		}
+
 		if (pos == NULL		     // mark doesn't exist
 			|| pos->lnum <= 0)   // mark isn't set in reg_buf
 		{
diff --git a/src/testdir/test_regexp_latin.vim b/src/testdir/test_regexp_latin.vim
index 71915be..fc9c81b 100644
--- a/src/testdir/test_regexp_latin.vim
+++ b/src/testdir/test_regexp_latin.vim
@@ -1042,10 +1042,17 @@
 
 func Test_using_mark_position()
   " this was using freed memory
+  " new engine
   new
   norm O0
   call assert_fails("s/\\%')", 'E486:')
   bwipe!
+
+  " old engine
+  new
+  norm O0
+  call assert_fails("s/\\%#=1\\%')", 'E486:')
+  bwipe!
 endfunc
 
 func Test_using_visual_position()
diff --git a/src/version.c b/src/version.c
index 03778bd..14fd1c3 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4646,
+/**/
     4645,
 /**/
     4644,