diff --git a/src/screen.cpp b/src/screen.cpp
index abb043859..7ef17100b 100644
--- a/src/screen.cpp
+++ b/src/screen.cpp
@@ -1220,6 +1220,8 @@ void screen_t::write(const wcstring &left_prompt, const wcstring &right_prompt,
         cursor_arr = this->desired.cursor;
     }
 
+    int full_line_count = this->desired.cursor.y + 1;
+
     // Now that we've output everything, set the cursor to the position that we saved in the loop
     // above.
     this->desired.cursor = cursor_arr;
@@ -1231,7 +1233,6 @@ void screen_t::write(const wcstring &left_prompt, const wcstring &right_prompt,
 
     // Re-render our completions page if necessary. Limit the term size of the pager to the true
     // term size, minus the number of lines consumed by our string.
-    int full_line_count = cursor_arr.y + 1;
     pager.set_term_size(termsize_t{std::max(1, curr_termsize.width),
                                    std::max(1, curr_termsize.height - full_line_count)});
     pager.update_rendering(&page_rendering);
diff --git a/tests/checks/tmux-complete.fish b/tests/checks/tmux-complete.fish
index bad378881..2fc607551 100644
--- a/tests/checks/tmux-complete.fish
+++ b/tests/checks/tmux-complete.fish
@@ -28,3 +28,14 @@ isolated-tmux capture-pane -p
 # The "bc" part is the autosuggestion - we could use "capture-pane -e" to check colors.
 # CHECK: prompt 2> foo2 aabc
 # CHECK: aabc  aaBd
+
+# Check that a larger-than-screen completion list does not stomp a multiline commandline (#8509).
+isolated-tmux send-keys C-u 'complete -c foo3 -fa "(seq $LINES)\t(string repeat -n $COLUMNS d)"' Enter \
+    C-l begin Enter foo3 Enter "echo some trailing line" \
+    C-p C-e Space Tab Tab
+tmux-sleep
+isolated-tmux capture-pane -p | sed -n '1p;$p'
+# Assert that we didn't change the command line.
+# CHECK: prompt 3> begin
+# Also ensure that the pager is actually fully disclosed.
+# CHECK: rows 1 to 6 of 10