diff --git a/news/changelog-1.9.md b/news/changelog-1.9.md
index 8c1e5fafb8..a4bc16030f 100644
--- a/news/changelog-1.9.md
+++ b/news/changelog-1.9.md
@@ -197,6 +197,7 @@ All changes included in 1.9:
 - ([#13528](https://github.com/quarto-dev/quarto-cli/pull/13528)): Adds support for table specification using nested lists and the `list-table` class.
 - ([#13575](https://github.com/quarto-dev/quarto-cli/pull/13575)): Improve CPU architecture detection/reporting in macOS to allow quarto to run in virtualized environments such as OpenAI's `codex`.
 - ([#13656](https://github.com/quarto-dev/quarto-cli/issues/13656)): Fix R code cells with empty `lang: ""` option producing invalid markdown class attributes.
+- ([#13776](https://github.com/quarto-dev/quarto-cli/issues/13776)): Do not process tblwidths attributes for non-simple tables, since this breaks rowspan handling.
 - ([#13832](https://github.com/quarto-dev/quarto-cli/pull/13832)): Fix `license.text` metadata not being accessible when using an inline license (`license: "text"`), and populate it with the license name for CC licenses instead of empty string. (author: @mcanouil)
 - ([#13856](https://github.com/quarto-dev/quarto-cli/issues/13856)): Add code annotation support for Typst and Observable.js code blocks. (author: @mcanouil)
 - ([#13890](https://github.com/quarto-dev/quarto-cli/issues/13890)): Fix render failure when using `embed-resources: true` with input path through a symlinked directory. The cleanup now resolves symlinks before comparing paths.
diff --git a/src/resources/filters/modules/import_all.lua b/src/resources/filters/modules/import_all.lua
index ce87e0c489..61429636fc 100644
--- a/src/resources/filters/modules/import_all.lua
+++ b/src/resources/filters/modules/import_all.lua
@@ -21,7 +21,8 @@ _quarto.modules = {
   string = require("modules/string"),
   tablecolwidths = require("modules/tablecolwidths"),
   typst = require("modules/typst"),
-  listtable = require("modules/listtable")
+  listtable = require("modules/listtable"),
+  tableutils = require("modules/tableutils"),
 }
 
 quarto.brand = _quarto.modules.brand
diff --git a/src/resources/filters/modules/tablecolwidths.lua b/src/resources/filters/modules/tablecolwidths.lua
index 6f7091ef5e..f7adc938be 100644
--- a/src/resources/filters/modules/tablecolwidths.lua
+++ b/src/resources/filters/modules/tablecolwidths.lua
@@ -83,6 +83,22 @@ local function tblColwidthValues(tbl, tblColwidths)
 end
 
 local function resolve_table_colwidths_scoped(tbl, scope)
+  local all_cells = require("modules/tableutils").all_cells
+  local function is_simple(tbl)
+    for cell in all_cells(tbl) do
+        if cell.col_span ~= 1 or cell.row_span ~= 1 then
+            return false
+        end        
+    end
+    return true
+  end
+  -- https://github.com/quarto-dev/quarto-cli/issues/13776: do
+  -- not process a table with to_simple_table/from_simple_table
+  -- roundtrip is table isn't simple
+  if not is_simple(tbl) then
+    return nil
+  end
+
   -- see if we have a tbl-colwidths attribute
   local tblColwidths = nil
   if tbl.caption.long ~= nil and #tbl.caption.long > 0 then
diff --git a/src/resources/filters/modules/tableutils.lua b/src/resources/filters/modules/tableutils.lua
new file mode 100644
index 0000000000..5b759acc73
--- /dev/null
+++ b/src/resources/filters/modules/tableutils.lua
@@ -0,0 +1,33 @@
+return {
+  all_cells = function (tbl)
+    return coroutine.wrap(function()
+      -- head rows
+      for _, row in ipairs(tbl.head.rows) do
+        for _, cell in ipairs(row.cells) do
+          coroutine.yield(cell)
+        end
+      end
+      -- body sections
+      for _, body in ipairs(tbl.bodies) do
+        -- intermediate head rows
+        for _, row in ipairs(body.head) do
+          for _, cell in ipairs(row.cells) do
+            coroutine.yield(cell)
+          end
+        end
+        -- body rows
+        for _, row in ipairs(body.body) do
+          for _, cell in ipairs(row.cells) do
+            coroutine.yield(cell)
+          end
+        end
+      end
+      -- foot rows
+      for _, row in ipairs(tbl.foot.rows) do
+        for _, cell in ipairs(row.cells) do
+          coroutine.yield(cell)
+        end
+      end
+    end)
+  end
+}
\ No newline at end of file
diff --git a/tests/docs/smoke-all/2026/02/23/issue-13776.qmd b/tests/docs/smoke-all/2026/02/23/issue-13776.qmd
new file mode 100644
index 0000000000..345e7a6002
--- /dev/null
+++ b/tests/docs/smoke-all/2026/02/23/issue-13776.qmd
@@ -0,0 +1,28 @@
+---
+format: html
+title: Hello
+_quarto:
+  tests:
+    html:
+      ensureFileRegexMatches:
+        - 
+          - "rowspan.*2.*Yes rows"
+        -
+          - "rowspan.*2.*No rows"
+---
+
++--------------+----------------------+
+| Col1         | Col2                 |
++==============+======================+
+| **Yes rows** | <http://example.com> |
+|              +----------------------+
+|              | Row2                 |
++--------------+----------------------+
+
++-------------+----------------------+
+| Col1        | Col2                 |
++=============+======================+
+| **No rows** | <http://example.com> |
++-------------+----------------------+
+|             | Row2                 |
++-------------+----------------------+