diff --git a/docs/changelog.rst b/docs/changelog.rst
index a9ab48f60..502ee0119 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -107,6 +107,9 @@ Detailed list of changes
   documents that point to executable files. Can be overridden by specifying
   your own :file:`launch-actions.conf`.
 
+- Fix a regression in version 0.40.0 causing a crash when the underline
+  thickness of the font is zero (:iss:`8443`)
+
 
 0.40.1 [2025-03-18]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/kitty/decorations.c b/kitty/decorations.c
index 0ec3bbfee..8ba1fa9f9 100644
--- a/kitty/decorations.c
+++ b/kitty/decorations.c
@@ -100,7 +100,7 @@ distribute_dots(unsigned available_space, unsigned num_of_dots, unsigned *summed
 
 DecorationGeometry
 add_dotted_underline(uint8_t *buf, FontCellMetrics fcm) {
-    unsigned num_of_dots = MAX(1u, fcm.cell_width / (2 * fcm.underline_thickness));
+    unsigned num_of_dots = MAX(1u, fcm.cell_width / (2 * MAX(1u, fcm.underline_thickness)));
     RAII_ALLOC(unsigned, spacing, malloc(num_of_dots * 2 * sizeof(unsigned)));
     if (!spacing) fatal("Out of memory");
     unsigned size = distribute_dots(fcm.cell_width, num_of_dots, spacing, spacing + num_of_dots);