diff --git a/docs/changelog.rst b/docs/changelog.rst
index 5e54496a0..149a2e384 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -202,6 +202,8 @@ Detailed list of changes
 0.49.0 [future]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
+- Thai/Lao: Render the vowel sign AM (U+0E33/U+0EB3) correctly by widening the cell it combines into, matching wcwidth() based programs
+
 - Support for :doc:`/custom-shaders` for adding various graphical effects (:iss:`10344`)
 
 - Various throughput performance improvements for a 15-35% real world improvement depending on workload
diff --git a/docs/text-sizing-protocol.rst b/docs/text-sizing-protocol.rst
index 360da6c79..83f9ef5a1 100644
--- a/docs/text-sizing-protocol.rst
+++ b/docs/text-sizing-protocol.rst
@@ -412,7 +412,10 @@ For each decoded code point:
 
 #. If there is no boundary, the current code point is added to the previous
    cell and processing of the code point is finished. See the :ref:`var_select`
-   section below for handling of Unicode Variation selectors.
+   section below for handling of Unicode Variation selectors. If the code point has
+   ``Grapheme_Cluster_Break=SpacingMark`` and a non-zero width and the previous
+   cell is one cell wide, the previous cell becomes two cells wide. This affects
+   only :code:`U+0E33 THAI CHARACTER SARA AM` and :code:`U+0EB3 LAO VOWEL SIGN AM`.
 
 #. If there is a boundary, but the width of the current code point is zero,
    it is added to the previous cell and processing is finished.
diff --git a/kitty/screen.c b/kitty/screen.c
index c8c2c439e..72a4947d8 100644
--- a/kitty/screen.c
+++ b/kitty/screen.c
@@ -1172,6 +1172,32 @@ move_widened_char_past_multiline_chars(Screen *self, text_loop_state *s, CPUCell
     else init_text_loop_line(self, s);
 }
 
+static void
+widen_cell_to_two(Screen *self, text_loop_state *s, CPUCell *cp, GPUCell *gp, index_type xpos) {
+    CPUCell *cpu_cell = cp + xpos;
+    GPUCell *gpu_cell = gp + xpos;
+    cpu_cell->is_multicell = true;
+    cpu_cell->width = 2;
+    cpu_cell->natural_width = true;
+    if (!cpu_cell->scale) cpu_cell->scale = 1;
+    if (xpos + 1 < self->columns) {
+        CPUCell *second = cp + xpos + 1;
+        if (second->is_multicell) {
+            if (second->y) {
+                move_widened_char_past_multiline_chars(self, s, cpu_cell, gpu_cell, xpos, s->prev.y);
+                return;
+            }
+            nuke_multicell_char_at(self, xpos + 1, s->prev.y, false);
+        }
+        zero_cells(s, second, gp + xpos + 1);
+        self->cursor->x++;
+        *second = *cpu_cell;
+        second->x = 1;
+    } else {
+        move_widened_char_past_multiline_chars(self, s, cpu_cell, gpu_cell, xpos, s->prev.y);
+    }
+}
+
 static bool
 is_emoji_presentation_base(char_type ch) {
     return char_props_for(ch).is_emoji_presentation_base == 1;
@@ -1187,29 +1213,8 @@ draw_combining_char(Screen *self, text_loop_state *s, char_type ch) {
     if (!add_combining_char(self, ch, xpos, s->prev.y) || self->lc->count < 2) return;
     unsigned base_pos = self->lc->count - 2;
     if (ch == VS16) { // emoji presentation variation marker makes default text presentation emoji (narrow emoji) into wide emoji
-        CPUCell *cpu_cell = cp + xpos;
-        GPUCell *gpu_cell = gp + xpos;
-        if (self->lc->chars[base_pos + 1] == VS16 && !cpu_cell->is_multicell && is_emoji_presentation_base(self->lc->chars[base_pos])) {
-            cpu_cell->is_multicell = true;
-            cpu_cell->width = 2;
-            cpu_cell->natural_width = true;
-            if (!cpu_cell->scale) cpu_cell->scale = 1;
-            if (xpos + 1 < self->columns) {
-                CPUCell *second = cp + xpos + 1;
-                if (second->is_multicell) {
-                    if (second->y) {
-                        move_widened_char_past_multiline_chars(self, s, cpu_cell, gpu_cell, xpos, s->prev.y);
-                        return;
-                    }
-                    nuke_multicell_char_at(self, xpos + 1, s->prev.y, false);
-                }
-                zero_cells(s, second, gp + xpos + 1);
-                self->cursor->x++;
-                *second = *cpu_cell;
-                second->x = 1;
-            } else {
-                move_widened_char_past_multiline_chars(self, s, cpu_cell, gpu_cell, xpos, s->prev.y);
-            }
+        if (self->lc->chars[base_pos + 1] == VS16 && !cp[xpos].is_multicell && is_emoji_presentation_base(self->lc->chars[base_pos])) {
+            widen_cell_to_two(self, s, cp, gp, xpos);
         }
     } else if (ch == VS15) {
         const CPUCell *cpu_cell = cp + xpos;
@@ -1220,6 +1225,10 @@ draw_combining_char(Screen *self, text_loop_state *s, char_type ch) {
                 init_segmentation_state(self, s);
             }
         }
+    } else {
+        // Thai/Lao SARA AM is a SpacingMark with non-zero width, it widens a narrow base cell
+        CharProps ch_props = char_props_for(ch);
+        if (ch_props.grapheme_break == GBP_SpacingMark && wcwidth_std(ch_props) > 0 && !cp[xpos].is_multicell) widen_cell_to_two(self, s, cp, gp, xpos);
     }
 }
 
diff --git a/kitty/wcswidth.c b/kitty/wcswidth.c
index d758a14bb..4fcaa5f9c 100644
--- a/kitty/wcswidth.c
+++ b/kitty/wcswidth.c
@@ -49,6 +49,13 @@ wcswidth_step(WCSState *state, const char_type ch) {
                             state->prev_width = 1;
                         } else state->prev_width = 0;
                         break;
+                    default:
+                        // Thai/Lao SARA AM: a SpacingMark with non-zero width widens a narrow base cell
+                        if (cp.grapheme_break == GBP_SpacingMark && wcwidth_std(cp) > 0 && state->prev_width == 1) {
+                            ans = 1;
+                            state->prev_width = 2;
+                        }
+                        break;
                 }
                 break;
             }
diff --git a/kitty_tests/datatypes.py b/kitty_tests/datatypes.py
index bfd92009a..abe82c397 100644
--- a/kitty_tests/datatypes.py
+++ b/kitty_tests/datatypes.py
@@ -578,6 +578,12 @@ class TestDataTypes(BaseTest):
         self.ae(wcswidth('\U0001f610\ufe0e'), 1)
         self.ae(wcswidth('\U0001f1e6a'), 3)
         self.ae(wcswidth('\U0001f1e6a\U0001f1e8a'), 6)
+        # Thai/Lao SARA AM is a SpacingMark with width 1, it widens the cell it combines into
+        self.ae(wcswidth('จำ'), 2)
+        self.ae(wcswidth('ำ'), 1)
+        self.ae(wcswidth('กิ'), 1)
+        self.ae(wcswidth('จำำ'), 2)
+        self.ae(wcswidth('ກຳ'), 2)
         self.ae(wcswidth('\U0001f1e6\U0001f1e8a'), 3)
         self.ae(wcswidth('\U0001f1e6\U0001f1e8\U0001f1e6'), 4)
         self.ae(wcswidth('a\u00adb'), 2)
diff --git a/kitty_tests/screen.py b/kitty_tests/screen.py
index 8242584a5..fd81a7a86 100644
--- a/kitty_tests/screen.py
+++ b/kitty_tests/screen.py
@@ -1067,6 +1067,38 @@ class TestScreen(BaseTest):
         s.reset()
         s.draw('\N{HEAVY EXCLAMATION MARK SYMBOL}' + 4500 * '\N{VARIATION SELECTOR-16}')
 
+    def test_spacing_mark_widens_narrow_cell(self):
+        # Thai SARA AM and Lao AM are SpacingMarks with width 1 that widen the cell they combine into
+        s = self.create_screen(cols=5)
+        s.draw('จำ')
+        self.ae(s.cursor.x, 2)
+        self.assertTrue(str(s.line(0)).startswith('จำ'))
+        c = s.cpu_cells(0, 0)
+        self.assertTrue(c['mcd'])
+        self.ae(c['mcd']['width'], 2)
+        self.ae(c['x'], 0)
+        self.ae(s.cpu_cells(0, 1)['x'], 1)
+        s.reset()
+        s.draw('จ')
+        self.ae(s.cursor.x, 1)
+        s.draw('ำ')
+        self.ae(s.cursor.x, 2)
+        s.reset()
+        s.draw('จำำ')
+        self.ae(s.cursor.x, 2)
+        s.reset()
+        s.draw('ກຳ')
+        self.ae(s.cursor.x, 2)
+        s.reset()
+        s.draw('กิ')
+        self.ae(s.cursor.x, 1)
+        # widened char on the last column wraps onto the next line
+        s = self.create_screen(cols=2)
+        s.draw('aจำ')
+        self.ae((s.cursor.x, s.cursor.y), (2, 1))
+        self.ae(str(s.line(0)), 'a')
+        self.ae(str(s.line(1)), 'จำ')
+
     def test_writing_with_cursor_on_trailer_of_wide_character(self):
         s = self.create_screen()
 
diff --git a/tools/wcswidth/wcswidth.go b/tools/wcswidth/wcswidth.go
index 332ac08f6..bc736ed4a 100644
--- a/tools/wcswidth/wcswidth.go
+++ b/tools/wcswidth/wcswidth.go
@@ -84,6 +84,12 @@ func (self *WCWidthIterator) handle_rune(ch rune) error {
 				self.current_width -= 1
 				self.prev_width = 1
 			}
+		default:
+			// Thai/Lao SARA AM: a SpacingMark with non-zero width widens a narrow base cell
+			if cp.Grapheme_break() == uint8(GBP_SpacingMark) && cp.Width() > 0 && self.prev_width == 1 {
+				self.current_width += 1
+				self.prev_width = 2
+			}
 		}
 	} else {
 		width := cp.Width()
diff --git a/tools/wcswidth/wcswidth_test.go b/tools/wcswidth/wcswidth_test.go
index fd283b89a..3ab81cee5 100644
--- a/tools/wcswidth/wcswidth_test.go
+++ b/tools/wcswidth/wcswidth_test.go
@@ -36,6 +36,12 @@ func TestWCSWidth(t *testing.T) {
 	wcswidth("\U0001F1E6\U0001F1E8a", 3)
 	wcswidth("\U0001F1E6\U0001F1E8\U0001F1E6", 4)
 	wcswidth("a\u00adb", 2)
+	// Thai/Lao SARA AM is a SpacingMark with width 1, it widens the cell it combines into
+	wcswidth("จำ", 2)
+	wcswidth("ำ", 1)
+	wcswidth("กิ", 1)
+	wcswidth("จำำ", 2)
+	wcswidth("ກຳ", 2)
 	wcswidth("a\x1b[22bcd", 25)
 	// Flags individually and together
 	wcwidth("\U0001f1ee\U0001f1f3", 2, 2)