diff --git a/demos/er.html b/demos/er.html
index 124311a032..a1c9e20069 100644
--- a/demos/er.html
+++ b/demos/er.html
@@ -57,6 +57,20 @@
         number final_price
       }
     </pre>
+    <hr />
+
+    <pre class="mermaid">
+    erDiagram
+      "HOSPITAL" {
+        int id PK
+        int doctor_id FK
+        string address UK
+        string name
+        string phone_number
+        string fax_number
+      }
+    </pre>
+    <hr />
 
     <script src="./mermaid.js"></script>
     <script type="module">
diff --git a/docs/syntax/entityRelationshipDiagram.md b/docs/syntax/entityRelationshipDiagram.md
index 4f33b1edc7..447b8d3227 100644
--- a/docs/syntax/entityRelationshipDiagram.md
+++ b/docs/syntax/entityRelationshipDiagram.md
@@ -234,14 +234,14 @@ The `type` and `name` values must begin with an alphabetic character and may con
 
 #### Attribute Keys and Comments
 
-Attributes may also have a `key` or comment defined. Keys can be "PK" or "FK", for Primary Key or Foreign Key. And a `comment` is defined by double quotes at the end of an attribute. Comments themselves cannot have double-quote characters in them.
+Attributes may also have a `key` or comment defined. Keys can be "PK", "FK" or "UK", for Primary Key, Foreign Key or Unique Key. And a `comment` is defined by double quotes at the end of an attribute. Comments themselves cannot have double-quote characters in them.
 
 ```mermaid-example
 erDiagram
     CAR ||--o{ NAMED-DRIVER : allows
     CAR {
         string allowedDriver FK "The license of the allowed driver"
-        string registrationNumber
+        string registrationNumber UK
         string make
         string model
         string[] parts
@@ -261,7 +261,7 @@ erDiagram
     CAR ||--o{ NAMED-DRIVER : allows
     CAR {
         string allowedDriver FK "The license of the allowed driver"
-        string registrationNumber
+        string registrationNumber UK
         string make
         string model
         string[] parts
diff --git a/packages/mermaid/src/diagrams/er/parser/erDiagram.jison b/packages/mermaid/src/diagrams/er/parser/erDiagram.jison
index bd8dc20f09..ada176a8d4 100644
--- a/packages/mermaid/src/diagrams/er/parser/erDiagram.jison
+++ b/packages/mermaid/src/diagrams/er/parser/erDiagram.jison
@@ -29,7 +29,7 @@ accDescr\s*"{"\s*                                { this.begin("acc_descr_multili
 "erDiagram"                     return 'ER_DIAGRAM';
 "{"                             { this.begin("block"); return 'BLOCK_START'; }
 <block>\s+                      /* skip whitespace in block */
-<block>\b((?:PK)|(?:FK))\b      return 'ATTRIBUTE_KEY'
+<block>\b((?:PK)|(?:FK)|(?:UK))\b      return 'ATTRIBUTE_KEY'
 <block>(.*?)[~](.*?)*[~]        return 'ATTRIBUTE_WORD';
 <block>[A-Za-z][A-Za-z0-9\-_\[\]\(\)]*  return 'ATTRIBUTE_WORD'
 <block>\"[^"]*\"                return 'COMMENT';
diff --git a/packages/mermaid/src/diagrams/er/parser/erDiagram.spec.js b/packages/mermaid/src/diagrams/er/parser/erDiagram.spec.js
index e472f51226..ba00c602e3 100644
--- a/packages/mermaid/src/diagrams/er/parser/erDiagram.spec.js
+++ b/packages/mermaid/src/diagrams/er/parser/erDiagram.spec.js
@@ -176,17 +176,18 @@ describe('when parsing ER diagram it...', function () {
     expect(entities[entity].attributes.length).toBe(1);
   });
 
-  it('should allow an entity with attribute starting with fk or pk and a comment', function () {
+  it('should allow an entity with attribute starting with fk, pk or uk and a comment', function () {
     const entity = 'BOOK';
     const attribute1 = 'int fk_title FK';
     const attribute2 = 'string pk_author PK';
-    const attribute3 = 'float pk_price PK "comment"';
+    const attribute3 = 'string uk_address UK';
+    const attribute4 = 'float pk_price PK "comment"';
 
     erDiagram.parser.parse(
-      `erDiagram\n${entity} {\n${attribute1} \n\n${attribute2}\n${attribute3}\n}`
+      `erDiagram\n${entity} {\n${attribute1} \n\n${attribute2}\n${attribute3}\n${attribute4}\n}`
     );
     const entities = erDb.getEntities();
-    expect(entities[entity].attributes.length).toBe(3);
+    expect(entities[entity].attributes.length).toBe(4);
   });
 
   it('should allow an entity with attribute that has a generic type', function () {
diff --git a/packages/mermaid/src/docs/syntax/entityRelationshipDiagram.md b/packages/mermaid/src/docs/syntax/entityRelationshipDiagram.md
index d83fd4b098..e136cb31ab 100644
--- a/packages/mermaid/src/docs/syntax/entityRelationshipDiagram.md
+++ b/packages/mermaid/src/docs/syntax/entityRelationshipDiagram.md
@@ -164,14 +164,14 @@ The `type` and `name` values must begin with an alphabetic character and may con
 
 #### Attribute Keys and Comments
 
-Attributes may also have a `key` or comment defined. Keys can be "PK" or "FK", for Primary Key or Foreign Key. And a `comment` is defined by double quotes at the end of an attribute. Comments themselves cannot have double-quote characters in them.
+Attributes may also have a `key` or comment defined. Keys can be "PK", "FK" or "UK", for Primary Key, Foreign Key or Unique Key. And a `comment` is defined by double quotes at the end of an attribute. Comments themselves cannot have double-quote characters in them.
 
 ```mermaid-example
 erDiagram
     CAR ||--o{ NAMED-DRIVER : allows
     CAR {
         string allowedDriver FK "The license of the allowed driver"
-        string registrationNumber
+        string registrationNumber UK
         string make
         string model
         string[] parts