diff --git a/src/nvim/memline.c b/src/nvim/memline.c
index 57b6b1b79a..6ef3a69b9a 100644
--- a/src/nvim/memline.c
+++ b/src/nvim/memline.c
@@ -2487,23 +2487,19 @@ void ml_add_deleted_len_buf(buf_T *buf, char *ptr, ssize_t len)
   }
 }
 
+/// Replace line "lnum", with buffering, in current buffer.
 int ml_replace(linenr_T lnum, char *line, bool copy)
 {
   return ml_replace_buf(curbuf, lnum, line, copy, false);
 }
 
-/// Replace line "lnum", with buffering, in current buffer.
-///
-/// @param copy  if true, make a copy of the line, otherwise the line has been
-///              copied to allocated memory already.
-///              if false, the "line" may be freed to add text properties!
-///
-/// Do not use it after calling ml_replace().
-///
-/// Check: The caller of this function should probably also call
-/// changed_lines(), unless update_screen(UPD_NOT_VALID) is used.
-///
-/// @return  FAIL for failure, OK otherwise
+/// Replace a line for the current buffer.  Like ml_replace() with:
+/// "len" is the length of the text, excluding NUL.
+int ml_replace_len(linenr_T lnum, char *line, size_t len, bool copy)
+{
+  return ml_replace_buf_len(curbuf, lnum, line, len, copy, false);
+}
+
 int ml_replace_buf(buf_T *buf, linenr_T lnum, char *line, bool copy, bool noalloc)
   FUNC_ATTR_NONNULL_ARG(1)
 {
@@ -2511,6 +2507,19 @@ int ml_replace_buf(buf_T *buf, linenr_T lnum, char *line, bool copy, bool noallo
   return ml_replace_buf_len(buf, lnum, line, len, copy, noalloc);
 }
 
+/// Replace line "lnum", with buffering.
+///
+/// @param copy  if true, make a copy of the line, otherwise the line has been
+///              copied to allocated memory already.
+///              if false, the "line" may be freed to add text properties!
+/// @param len_arg  length of the text, excluding NUL
+///
+/// Do not use it after calling ml_replace().
+///
+/// Check: The caller of this function should probably also call
+/// changed_lines(), unless update_screen(UPD_NOT_VALID) is used.
+///
+/// @return  FAIL for failure, OK otherwise
 int ml_replace_buf_len(buf_T *buf, linenr_T lnum, char *line_arg, size_t len_arg, bool copy,
                        bool noalloc)
   FUNC_ATTR_NONNULL_ARG(1)
diff --git a/src/nvim/ops.c b/src/nvim/ops.c
index 61f94172e2..25dd40a793 100644
--- a/src/nvim/ops.c
+++ b/src/nvim/ops.c
@@ -4014,9 +4014,9 @@ int do_join(size_t count, bool insert_space, bool save_undo, bool use_formatopti
   colnr_T col = sumsize - currsize - spaces[count - 1];
 
   // allocate the space for the new line
-  char *newp = xmalloc((size_t)sumsize + 1);
+  size_t newp_len = (size_t)sumsize;
+  char *newp = xmallocz(newp_len);
   cend = newp + sumsize;
-  *cend = 0;
 
   // Move affected lines to the new long one.
   // This loops backwards over the joined lines, including the original line.
@@ -4030,6 +4030,7 @@ int do_join(size_t count, bool insert_space, bool save_undo, bool use_formatopti
   for (linenr_T t = (linenr_T)count - 1;; t--) {
     cend -= currsize;
     memmove(cend, curr, (size_t)currsize);
+
     if (spaces[t] > 0) {
       cend -= spaces[t];
       memset(cend, ' ', (size_t)(spaces[t]));
@@ -4060,7 +4061,7 @@ int do_join(size_t count, bool insert_space, bool save_undo, bool use_formatopti
     currsize = (int)strlen(curr);
   }
 
-  ml_replace(curwin->w_cursor.lnum, newp, false);
+  ml_replace_len(curwin->w_cursor.lnum, newp, newp_len, false);
 
   if (setmark && (cmdmod.cmod_flags & CMOD_LOCKMARKS) == 0) {
     // Set the '] mark.