diff --git a/blocks/api/serializer.js b/blocks/api/serializer.js
index a29c1fedaa46af..280f9dfcb49464 100644
--- a/blocks/api/serializer.js
+++ b/blocks/api/serializer.js
@@ -59,7 +59,7 @@ export function getCommentAttributes( realAttributes, expectedAttributes ) {
 			return memo;
 		}
 
-		return memo + `${ key }:${ value } `;
+		return memo + `${ key }="${ value }" `;
 	}, '' );
 }
 
diff --git a/blocks/api/test/serializer.js b/blocks/api/test/serializer.js
index d639d320428116..59a71ca0f5199e 100644
--- a/blocks/api/test/serializer.js
+++ b/blocks/api/test/serializer.js
@@ -71,7 +71,7 @@ describe( 'block serializer', () => {
 				fruit: 'bananas'
 			} );
 
-			expect( attributes ).to.equal( 'category:food ripeness:ripe ' );
+			expect( attributes ).to.equal( 'category="food" ripeness="ripe" ' );
 		} );
 
 		it( 'should not append an undefined attribute value', () => {
@@ -83,7 +83,7 @@ describe( 'block serializer', () => {
 				fruit: 'bananas'
 			} );
 
-			expect( attributes ).to.equal( 'category:food ' );
+			expect( attributes ).to.equal( 'category="food" ' );
 		} );
 	} );
 
@@ -109,7 +109,7 @@ describe( 'block serializer', () => {
 					}
 				}
 			];
-			const expectedPostContent = '<!-- wp:core/test-block align:left -->\n<p>Ribs & Chicken</p>\n<!-- /wp:core/test-block -->\n\n';
+			const expectedPostContent = '<!-- wp:core/test-block align="left" -->\n<p>Ribs & Chicken</p>\n<!-- /wp:core/test-block -->\n\n';
 
 			expect( serialize( blockList ) ).to.eql( expectedPostContent );
 		} );