diff --git a/tsconfig.json b/tsconfig.json
index 56402e7..ea3f593 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -31,6 +31,11 @@
     "noImplicitThis": true,
     "strict": true,
 
+    // See <https://www.semver-ts.org/formal-spec/5-compiler-considerations.html#strictness>
+    // These 2 options are also part of the recommended tsconfig as of TS 5.9
+    "noUncheckedIndexedAccess": true,
+    "exactOptionalPropertyTypes": true,
+
     // <https://devblogs.microsoft.com/typescript/announcing-typescript-5-0/#verbatimmodulesyntax>
     // Any imports or exports without a type modifier are left around. This is important for `<script setup>`.
     // Anything that uses the type modifier is dropped entirely.
diff --git a/tsconfig.lib.json b/tsconfig.lib.json
index 964598a..1810eeb 100644
--- a/tsconfig.lib.json
+++ b/tsconfig.lib.json
@@ -8,6 +8,6 @@
     // Libraries generally require more strict type accuracy.
     // For example, its types must be compatible with the Vue types.
     // So we don't want to skip the type checking of its dependencies.
-    "skipLibCheck": false
+    "skipLibCheck": false,
   }
 }