diff --git a/src/lib.cpp b/src/lib.cpp
index 01c6936..24040f5 100644
--- a/src/lib.cpp
+++ b/src/lib.cpp
@@ -8,7 +8,7 @@ extern "C" {
 __attribute__((visibility("default"))) WeaselJsonParser *
 WeaselJsonParser_create(int stackSize, const WeaselJsonCallbacks *callbacks,
                         void *userdata) {
-  auto *buf = malloc(sizeof(Parser3) + stackSize);
+  auto *buf = malloc(sizeof(Parser3) + stackSize * sizeof(*Parser3::stackPtr));
   if (buf == nullptr) {
     return nullptr;
   }