diff --git a/ChangeLog.asciidoc b/ChangeLog.asciidoc
index 1856ff10f..0ec108c38 100644
--- a/ChangeLog.asciidoc
+++ b/ChangeLog.asciidoc
@@ -26,6 +26,8 @@ https://weechat.org/files/releasenotes/ReleaseNotes-devel.html[release notes]
 
 === Bugs fixed
 
+* core: fix truncated messages after a word with a length of zero on screen
+  (for example a zero width space: U+200B) (bug #40985, issue #502)
 * irc: fix display of messages sent to server in raw buffer
 * irc: fix display of invalid UTF-8 chars in raw buffer
 
diff --git a/src/gui/curses/gui-curses-chat.c b/src/gui/curses/gui-curses-chat.c
index c1cf10a82..0bbd1810e 100644
--- a/src/gui/curses/gui-curses-chat.c
+++ b/src/gui/curses/gui-curses-chat.c
@@ -1365,13 +1365,13 @@ gui_chat_display_line (struct t_gui_window *window, struct t_gui_line *line,
             ptr_end_offset = ptr_data + word_end_offset;
 
             /* if message ends with spaces, display them */
-            if ((word_length == 0) && (word_length_with_spaces > 0)
+            if ((word_length <= 0) && (word_length_with_spaces > 0)
                 && !ptr_data[word_end_offset + 1])
             {
                 word_length = word_length_with_spaces;
             }
 
-            if (word_length > 0)
+            if (word_length >= 0)
             {
                 line_align = gui_line_get_align (window->buffer, line, 1,
                                                  (lines_displayed == 0) ? 1 : 0);
diff --git a/src/gui/gui-chat.c b/src/gui/gui-chat.c
index 163e2d9c0..0c2ced0c7 100644
--- a/src/gui/gui-chat.c
+++ b/src/gui/gui-chat.c
@@ -332,7 +332,7 @@ gui_chat_get_word_info (struct t_gui_window *window,
     *word_start_offset = 0;
     *word_end_offset = 0;
     *word_length_with_spaces = 0;
-    *word_length = 0;
+    *word_length = -1;
 
     start_data = data;
 
@@ -354,6 +354,8 @@ gui_chat_get_word_info (struct t_gui_window *window,
                     *word_end_offset = next_char2 - start_data - 1;
                     char_size_screen = gui_chat_char_size_screen (next_char);
                     (*word_length_with_spaces) += char_size_screen;
+                    if (*word_length < 0)
+                        *word_length = 0;
                     (*word_length) += char_size_screen;
                 }
                 else