diff --git a/CHANGELOG.md b/CHANGELOG.md
index ecd6d3e..9900fe4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@
 - fix: Remove the extension's own label attribute when the output format gets no window chrome, so a writer that keeps attributes no longer prints it. (#63)
 - fix: Check every code block attribute in the code-window group against the schema, so a value nothing validated before, such as code-window-enabled, is now reported when it is wrong. The extension's own duplicate warnings for an invalid code-window-style or code-window-collapse are removed, since the schema already names the same mistake. (#60)
 - fix: Honour an explicit code-window-no-auto-filename="false", which previously suppressed auto-filename exactly like "true". (#60)
+- fix: Honour `code-window-collapse="false"` on a block, which could not turn off a document that sets `collapse`. The block fell back to the document setting and was folded anyway.
 - fix: Remove the extension's own duplicate collapse and style warnings at the document option level, now that the schema reports each mistake once. (#60)
 - fix: Match the code-window-collapse attribute schema to the string Pandoc always provides, so a documented "true" or "false" value no longer warns. (#60)
 - fix: Validate a code block's attributes on the HTML path the same way the Typst path already does, so an invalid attribute on a block holding executed-cell output is now reported on HTML too, instead of being silently accepted. (#60)
diff --git a/_extensions/code-window/code-window.lua b/_extensions/code-window/code-window.lua
index 55586c0..ca8c465 100644
--- a/_extensions/code-window/code-window.lua
+++ b/_extensions/code-window/code-window.lua
@@ -248,12 +248,20 @@ end
 --- test needed.
 --- @param resolved table<string, any> This block's attributes, resolved against the schema
 --- @return string|nil Resolved collapse mode ("open"/"closed") or nil when off
+--- @return boolean Whether this block decided, which is what separates an
+---   explicit "false" from an attribute the block never wrote
 local function read_block_collapse(resolved)
   local raw = resolved['code-window-collapse']
   if raw == nil then
-    return nil
+    return nil, false
+  end
+  local mode = VALID_COLLAPSE[raw]
+  if mode == nil then
+    -- A value the schema does not accept. The check reports it, and the
+    -- document option decides as though the block had written nothing.
+    return nil, false
   end
-  return resolve_collapse(raw)
+  return mode or nil, true
 end
 
 --- Read a highlight-lines spec from the block, looking at the
@@ -664,7 +672,11 @@ local function process_html(block, resolved, auto_label)
     return block
   end
 
-  local effective_collapse = read_block_collapse(resolved) or CONFIG.collapse
+  local block_collapse, block_decided = read_block_collapse(resolved)
+  local effective_collapse = block_collapse
+  if not block_decided then
+    effective_collapse = CONFIG.collapse
+  end
   local explicit_filename = block.attributes['filename']
 
   -- Add the marker classes and the chip the injected script reads. Both
@@ -673,8 +685,13 @@ local function process_html(block, resolved, auto_label)
     if overrides.style then
       table.insert(block.classes, 'cw-style-' .. overrides.style)
     end
+    -- A block that turned collapsing off is marked as well. The script reads
+    -- the absence of a marker as "this block said nothing" and falls back to
+    -- the document setting, so an opt-out needs a marker of its own.
     if effective_collapse then
       table.insert(block.classes, 'cw-collapse-' .. effective_collapse)
+    elseif block_decided and CONFIG.collapse then
+      table.insert(block.classes, 'cw-collapse-none')
     end
     if overrides.lines_label then
       block.attributes['code-window-lines-label'] = overrides.lines_label
@@ -755,8 +772,8 @@ document.addEventListener("DOMContentLoaded",function(){
     }
     var collapse=null;
     if(marker){
-      var cm=marker.className.match(/cw-collapse-(open|closed)/);
-      if(cm){collapse=cm[1];marker.classList.remove(cm[0]);}
+      var cm=marker.className.match(/cw-collapse-(open|closed|none)/);
+      if(cm){collapse=cm[1]==='none'?false:cm[1];marker.classList.remove(cm[0]);}
     }
     if(collapse===null&&DEFAULT_COLLAPSE){collapse=DEFAULT_COLLAPSE;}
     if(marker&&marker.hasAttribute("data-code-window-lines-label")){
diff --git a/tests/fixtures/collapse-block-off.qmd b/tests/fixtures/collapse-block-off.qmd
new file mode 100644
index 0000000..0788196
--- /dev/null
+++ b/tests/fixtures/collapse-block-off.qmd
@@ -0,0 +1,20 @@
+---
+title: "Collapse turned off for one block"
+format: html
+filters:
+  - code-window
+extensions:
+  code-window:
+    collapse: true
+---
+
+The document folds every block.
+The first block opts out, and the second takes the document setting.
+
+```{.python filename="opted-out.py" code-window-collapse="false"}
+x = 1
+```
+
+```{.python filename="inherits.py"}
+y = 2
+```
diff --git a/tests/run.sh b/tests/run.sh
index cae2fc8..7b060b5 100755
--- a/tests/run.sh
+++ b/tests/run.sh
@@ -280,6 +280,33 @@ else
 		"a #code-window( call in wrapper-default.typ"
 fi
 
+# ============================================================================
+# A block opts out of the document's collapse setting
+# ============================================================================
+
+render collapse-block-off html
+
+# The script folds a block that carries no marker, reading the absence as
+# "this block said nothing", so the opt-out is a marker of its own rather
+# than a missing one. The second block is here to show the two differ.
+collapse_markers="$(block_classes "${work_dir}/collapse-block-off.html" | grep -o 'cw-collapse-[a-z]*' | sort | tr '\n' ' ')"
+
+if [ "${collapse_markers}" = "cw-collapse-closed cw-collapse-none " ]; then
+	report pass "collapse-block-off: the block opts out and its neighbour does not"
+else
+	report fail "collapse-block-off: the block opts out and its neighbour does not" \
+		"cw-collapse-none on one block and cw-collapse-closed on the other, got: ${collapse_markers}"
+fi
+
+# The document setting still reaches the page, which is what the opt-out has
+# to override.
+if grep -q 'DEFAULT_COLLAPSE="closed"' "${work_dir}/collapse-block-off.html"; then
+	report pass "collapse-block-off: the document setting reaches the page"
+else
+	report fail "collapse-block-off: the document setting reaches the page" \
+		'DEFAULT_COLLAPSE="closed" in collapse-block-off.html'
+fi
+
 # ============================================================================
 
 printf '\n%s passed, %s failed\n' "${passed}" "${failed}"