diff --git a/src/testdir/test_vim9_cmd.vim b/src/testdir/test_vim9_cmd.vim
index 3b479f3..15c9a59 100644
--- a/src/testdir/test_vim9_cmd.vim
+++ b/src/testdir/test_vim9_cmd.vim
@@ -1172,5 +1172,27 @@
   CheckDefFailure(lines, 'E1178', 2)
 enddef
 
+def Test_substitute_expr()
+  var to = 'repl'
+  new
+  setline(1, 'one from two')
+  s/from/\=to
+  assert_equal('one repl two', getline(1))
+
+  setline(1, 'one from two')
+  s/from/\=to .. '_x'
+  assert_equal('one repl_x two', getline(1))
+
+  setline(1, 'one from two from three')
+  var also = 'also'
+  s/from/\=to .. '_' .. also/g#e
+  assert_equal('one repl_also two repl_also three', getline(1))
+
+  CheckDefFailure(['s/from/\="x")/'], 'E488:')
+  CheckDefFailure(['s/from/\="x"/9'], 'E488:')
+
+  bwipe!
+enddef
+
 
 " vim: ts=8 sw=2 sts=2 expandtab tw=80 fdm=marker
diff --git a/src/testdir/test_vim9_disassemble.vim b/src/testdir/test_vim9_disassemble.vim
index e6b3751..8a96bf2 100644
--- a/src/testdir/test_vim9_disassemble.vim
+++ b/src/testdir/test_vim9_disassemble.vim
@@ -121,6 +121,25 @@
         res)
 enddef
 
+def s:Substitute()
+  var expr = "abc"
+  :%s/a/\=expr/&g#c
+enddef
+
+def Test_disassemble_substitute()
+  var res = execute('disass s:Substitute')
+  assert_match('<SNR>\d*_Substitute.*' ..
+        ' var expr = "abc"\_s*' ..
+        '\d PUSHS "abc"\_s*' ..
+        '\d STORE $0\_s*' ..
+        ' :%s/a/\\=expr/&g#c\_s*' ..
+        '\d SUBSTITUTE   :%s/a/\\=expr/&g#c\_s*' ..
+        '    0 LOAD $0\_s*' ..
+        '    -------------\_s*' ..
+        '\d RETURN 0',
+        res)
+enddef
+
 def s:YankRange()
   norm! m[jjm]
   :'[,']yank