diff --git a/ts/tools/markpure.ts b/ts/tools/markpure.ts
index 534038cce..8d7b30463 100644
--- a/ts/tools/markpure.ts
+++ b/ts/tools/markpure.ts
@@ -39,7 +39,7 @@ function adjustFiles() {
         // strip out typeName info, which appears to only be required for
         // certain JSON functionality (though this only saves a few hundred
         // bytes)
-        newContents = contents.replace(typeRe, "$1(\"\",");
+        newContents = newContents.replace(typeRe, "$1(\"\",");
 
         if (contents != newContents) {
             fs.writeFileSync(file, newContents, "utf8");