diff --git a/packages/block-library/src/query/test/utils.js b/packages/block-library/src/query/test/utils.js
index e2619f2f70e88..8c2d88ade8051 100644
--- a/packages/block-library/src/query/test/utils.js
+++ b/packages/block-library/src/query/test/utils.js
@@ -68,6 +68,9 @@ describe( 'Query block utils', () => {
 
 	describe( 'getQueryContextFromTemplate', () => {
 		it( 'should return the correct query context based on template slug', () => {
+			expect( getQueryContextFromTemplate() ).toStrictEqual( {
+				isSingular: true,
+			} );
 			expect( getQueryContextFromTemplate( '404' ) ).toStrictEqual( {
 				isSingular: true,
 				templateType: '404',
diff --git a/packages/block-library/src/query/utils.js b/packages/block-library/src/query/utils.js
index ae1fccc6701e9..fc22ca46d471c 100644
--- a/packages/block-library/src/query/utils.js
+++ b/packages/block-library/src/query/utils.js
@@ -443,7 +443,11 @@ export const useUnsupportedBlocks = ( clientId ) => {
  * @param {string} templateSlug Current template slug based on context.
  * @return {Object} An object with isSingular and templateType properties.
  */
-export function getQueryContextFromTemplate( templateSlug = '' ) {
+export function getQueryContextFromTemplate( templateSlug ) {
+	// In the Post Editor, the template slug is not available.
+	if ( ! templateSlug ) {
+		return { isSingular: true };
+	}
 	let isSingular = false;
 	let templateType = templateSlug === 'wp' ? 'custom' : templateSlug;
 	const singularTemplates = [ '404', 'blank', 'single', 'page', 'custom' ];