diff --git a/index.js b/index.js
index 758245b..5187ae9 100644
--- a/index.js
+++ b/index.js
@@ -1,6 +1,6 @@
 /**
  * @typedef MarkdownTableOptions
- * @property {string|string[]} [align]
+ * @property {string|null|Array.<string|null|undefined>} [align]
  * @property {boolean} [padding=true]
  * @property {boolean} [delimiterStart=true]
  * @property {boolean} [delimiterStart=true]
@@ -12,7 +12,7 @@
 /**
  * Create a table from a matrix of strings.
  *
- * @param {string[][]} table
+ * @param {Array.<Array.<string|null|undefined>>} table
  * @param {MarkdownTableOptions} [options]
  * @returns {string}
  */
@@ -241,7 +241,7 @@ function defaultStringLength(value) {
 }
 
 /**
- * @param {string} value
+ * @param {string|null|undefined} value
  * @returns {number}
  */
 function toAlignment(value) {
diff --git a/tsconfig.json b/tsconfig.json
index 8ac10fe..e31adf8 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,5 +1,4 @@
 {
-  "files": ["index.js"],
   "include": ["*.js"],
   "compilerOptions": {
     "target": "ES2020",
@@ -11,6 +10,7 @@
     "declaration": true,
     "emitDeclarationOnly": true,
     "allowSyntheticDefaultImports": true,
-    "skipLibCheck": true
+    "skipLibCheck": true,
+    "strict": true
   }
 }