diff --git a/packages/feature-flags-webpack-plugin/src/index.ts b/packages/feature-flags-webpack-plugin/src/index.ts
index 6742f357..e5a1ffde 100644
--- a/packages/feature-flags-webpack-plugin/src/index.ts
+++ b/packages/feature-flags-webpack-plugin/src/index.ts
@@ -40,7 +40,9 @@ class FeatureFlagsWebpackPlugin {
     function onParseJavascript(parser: javascript.JavascriptParser) {
       parser.hooks.evaluate
         .for('CallExpression')
-        .tap('FeatureFlagsWebpackPlugin', (expression) => onCallExpression(expression, parser))
+        .tap('FeatureFlagsWebpackPlugin', (expression: Expression) =>
+          onCallExpression(expression, parser),
+        )
     }
 
     function onThisCompilation(_compilation: Compilation, compilationParams: any) {