diff --git a/demos/er.html b/demos/er.html
index 06fbf020e..a326185de 100644
--- a/demos/er.html
+++ b/demos/er.html
@@ -57,6 +57,20 @@ erDiagram
         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/packages/mermaid/src/diagrams/er/parser/erDiagram.jison b/packages/mermaid/src/diagrams/er/parser/erDiagram.jison
index f0411fd72..1cd1d62a0 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 43bc13e6d..83ae3f7ac 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 () {