diff --git a/packages/blocks/src/api/test/utils.js b/packages/blocks/src/api/test/utils.js
index 0bfeb8b0fe258..ea3fe57908441 100644
--- a/packages/blocks/src/api/test/utils.js
+++ b/packages/blocks/src/api/test/utils.js
@@ -67,5 +67,34 @@ describe( 'block helpers', () => {
 
 			expect( isUnmodifiedDefaultBlock( block ) ).toBe( false );
 		} );
+
+		it( 'should invalidate cache if the default block name changed', () => {
+			registerBlockType( 'core/test-block1', {
+				attributes: {
+					includesDefault1: {
+						type: 'boolean',
+						default: true,
+					},
+				},
+				save: noop,
+				category: 'common',
+				title: 'test block',
+			} );
+			registerBlockType( 'core/test-block2', {
+				attributes: {
+					includesDefault2: {
+						type: 'boolean',
+						default: true,
+					},
+				},
+				save: noop,
+				category: 'common',
+				title: 'test block',
+			} );
+			setDefaultBlockName( 'core/test-block1' );
+			isUnmodifiedDefaultBlock( createBlock( 'core/test-block1' ) );
+			setDefaultBlockName( 'core/test-block2' );
+			expect( isUnmodifiedDefaultBlock( createBlock( 'core/test-block2' ) ) ).toBe( true );
+		} );
 	} );
 } );
diff --git a/packages/blocks/src/api/utils.js b/packages/blocks/src/api/utils.js
index 392593b440096..6dcabbcbcea01 100644
--- a/packages/blocks/src/api/utils.js
+++ b/packages/blocks/src/api/utils.js
@@ -38,7 +38,16 @@ export function isUnmodifiedDefaultBlock( block ) {
 		return false;
 	}
 
-	const newDefaultBlock = createBlock( defaultBlockName );
+	// Cache a created default block if no cache exists or the default block
+	// name changed.
+	if (
+		! isUnmodifiedDefaultBlock.block ||
+		isUnmodifiedDefaultBlock.block.name !== defaultBlockName
+	) {
+		isUnmodifiedDefaultBlock.block = createBlock( defaultBlockName );
+	}
+
+	const newDefaultBlock = isUnmodifiedDefaultBlock.block;
 	const blockType = getBlockType( defaultBlockName );
 
 	return every( blockType.attributes, ( value, key ) =>