diff --git a/lib/schema.js b/lib/schema.js
index ea0d228..eb3695d 100644
--- a/lib/schema.js
+++ b/lib/schema.js
@@ -94,7 +94,7 @@ const parseIndexSpecification = (index, schemaSource) => {
                 sortKey = indexSpec.sortKey;
             }
         } else {
-            throw new Error('Invalid index specification ${indexSpec}: must be 1,true, or {hashKey:"", sortKey?:""}.');
+            throw new Error(`Invalid index specification ${JSON.stringify(indexSpec)}: must be 1, true, or {hashKey:"", sortKey?:""}.`);
         }
         indices.push({
             index,
diff --git a/test/schemas.js b/test/schemas.js
index 23c262e..64b3a92 100644
--- a/test/schemas.js
+++ b/test/schemas.js
@@ -909,7 +909,7 @@ t.test('schema errors', async t => {
                     aaa: false
                 }
             });
-        }, {message: 'Invalid index specification ${indexSpec}: must be 1,true, or {hashKey:"", sortKey?:""}.'} , 'should throw with key:false');
+        }, {message: 'Invalid index specification false: must be 1, true, or {hashKey:"", sortKey?:""}.'}, 'should throw with key:false');
 
         t.throws(() => {
             DynamoDM.Schema('namespace.shouldthrow', {