diff --git a/app/models/Comment.ts b/app/models/Comment.ts
index f7a35df35..1d7b05ae3 100644
--- a/app/models/Comment.ts
+++ b/app/models/Comment.ts
@@ -1,6 +1,7 @@
 import { subSeconds } from "date-fns";
 import { computed, observable } from "mobx";
 import { now } from "mobx-utils";
+import type { ProsemirrorData } from "@shared/types";
 import User from "~/models/User";
 import BaseModel from "./BaseModel";
 import Field from "./decorators/Field";
@@ -22,7 +23,7 @@ class Comment extends BaseModel {
    */
   @Field
   @observable
-  data: Record<string, any>;
+  data: ProsemirrorData;
 
   /**
    * If this comment is a reply then the parent comment will be set, otherwise
diff --git a/server/models/Comment.ts b/server/models/Comment.ts
index e6ac04fb4..8a65f5eb4 100644
--- a/server/models/Comment.ts
+++ b/server/models/Comment.ts
@@ -5,12 +5,16 @@ import {
   Column,
   Table,
   Scopes,
+  Length,
   DefaultScope,
 } from "sequelize-typescript";
+import type { ProsemirrorData } from "@shared/types";
+import { CommentValidation } from "@shared/validations";
 import Document from "./Document";
 import User from "./User";
 import ParanoidModel from "./base/ParanoidModel";
 import Fix from "./decorators/Fix";
+import TextLength from "./validators/TextLength";
 
 @DefaultScope(() => ({
   include: [
@@ -35,8 +39,16 @@ import Fix from "./decorators/Fix";
 @Table({ tableName: "comments", modelName: "comment" })
 @Fix
 class Comment extends ParanoidModel {
+  @TextLength({
+    max: CommentValidation.maxLength,
+    msg: `Comment must be less than ${CommentValidation.maxLength} characters`,
+  })
+  @Length({
+    max: CommentValidation.maxLength * 10,
+    msg: `Comment data is too large`,
+  })
   @Column(DataType.JSONB)
-  data: Record<string, any>;
+  data: ProsemirrorData;
 
   // associations
 
diff --git a/server/models/validators/TextLength.ts b/server/models/validators/TextLength.ts
new file mode 100644
index 000000000..f212f566d
--- /dev/null
+++ b/server/models/validators/TextLength.ts
@@ -0,0 +1,36 @@
+import { size } from "lodash";
+import { Node } from "prosemirror-model";
+import { addAttributeOptions } from "sequelize-typescript";
+import { ProsemirrorData } from "@shared/types";
+import ProsemirrorHelper from "@shared/utils/ProsemirrorHelper";
+import { schema } from "@server/editor";
+
+/**
+ * A decorator that validates the size of the text within a prosemirror data
+ * object, taking into account unicode characters of variable lengths.
+ */
+export default function TextLength({
+  msg,
+  min = 0,
+  max,
+}: {
+  msg?: string;
+  min?: number;
+  max: number;
+}): (target: any, propertyName: string) => void {
+  return (target: any, propertyName: string) =>
+    addAttributeOptions(target, propertyName, {
+      validate: {
+        validLength(value: ProsemirrorData) {
+          const text = ProsemirrorHelper.toPlainText(
+            Node.fromJSON(schema, value),
+            schema
+          );
+
+          if (size(text) > max || size(text) < min) {
+            throw new Error(msg);
+          }
+        },
+      },
+    });
+}
diff --git a/shared/types.ts b/shared/types.ts
index a7752acd8..9c2e8f9a5 100644
--- a/shared/types.ts
+++ b/shared/types.ts
@@ -208,3 +208,6 @@ export const NotificationEventDefaults = {
   [NotificationEventType.Features]: true,
   [NotificationEventType.ExportCompleted]: true,
 };
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export type ProsemirrorData = Record<string, any>;