diff --git a/lib/models/text.js b/lib/models/text.js
index fde1a2745..738ecd35f 100644
--- a/lib/models/text.js
+++ b/lib/models/text.js
@@ -287,14 +287,14 @@ class Text extends new Record(DEFAULTS) {
    */
 
   updateMark(index, length, mark, properties) {
+    const m = mark.merge(properties)
     const characters = this.characters.map((char, i) => {
       if (i < index) return char
       if (i >= index + length) return char
       let { marks } = char
-      const j = marks.indexOf(mark)
-      let m = marks.get(j)
-      m = m.merge(properties)
-      marks = marks.set(j, m)
+      if (!marks.has(mark)) return char
+      marks = marks.remove(mark)
+      marks = marks.add(m)
       char = char.merge({ marks })
       return char
     })
diff --git a/lib/transforms/apply-operation.js b/lib/transforms/apply-operation.js
index 74fb31469..3d80d3a5a 100644
--- a/lib/transforms/apply-operation.js
+++ b/lib/transforms/apply-operation.js
@@ -245,6 +245,7 @@ function setMark(state, operation) {
   let { document } = state
   let node = document.assertPath(path)
   node = node.updateMark(offset, length, mark, properties)
+  debugger
   document = document.updateDescendant(node)
   state = state.merge({ document })
   return state
diff --git a/test/transforms/fixtures/by-key/set-mark-by-key/set-data/index.js b/test/transforms/fixtures/by-key/set-mark-by-key/set-data/index.js
new file mode 100644
index 000000000..9c2a24bb3
--- /dev/null
+++ b/test/transforms/fixtures/by-key/set-mark-by-key/set-data/index.js
@@ -0,0 +1,21 @@
+
+export default function (state) {
+  const { document, selection } = state
+  const first = document.getTexts().first()
+
+  return state
+    .transform()
+    .setMarkByKey(
+      first.key,
+      0,
+      first.length,
+      {
+        type: 'bold',
+        data: { key: true }
+      },
+      {
+        data: { key: false }
+      }
+    )
+    .apply()
+}
diff --git a/test/transforms/fixtures/by-key/set-mark-by-key/set-data/input.yaml b/test/transforms/fixtures/by-key/set-mark-by-key/set-data/input.yaml
new file mode 100644
index 000000000..bc54126ff
--- /dev/null
+++ b/test/transforms/fixtures/by-key/set-mark-by-key/set-data/input.yaml
@@ -0,0 +1,12 @@
+
+nodes:
+  - kind: block
+    type: paragraph
+    nodes:
+      - kind: text
+        ranges:
+          - text: word
+            marks:
+              - type: bold
+                data:
+                  key: true
diff --git a/test/transforms/fixtures/by-key/set-mark-by-key/set-data/output.yaml b/test/transforms/fixtures/by-key/set-mark-by-key/set-data/output.yaml
new file mode 100644
index 000000000..88518e9d8
--- /dev/null
+++ b/test/transforms/fixtures/by-key/set-mark-by-key/set-data/output.yaml
@@ -0,0 +1,12 @@
+
+nodes:
+  - kind: block
+    type: paragraph
+    nodes:
+      - kind: text
+        ranges:
+          - text: word
+            marks:
+              - type: bold
+                data:
+                  key: false