diff --git a/src/parser3.h b/src/parser3.h
index 0390571..b7776c1 100644
--- a/src/parser3.h
+++ b/src/parser3.h
@@ -2,6 +2,7 @@
 
 #include <cassert>
 #include <cctype>
+#include <cstddef>
 #include <cstdint>
 #include <cstdio>
 #include <cstring>
@@ -63,7 +64,8 @@ enum Symbol : uint8_t {
 };
 struct Parser3 {
   Parser3(const WeaselJsonCallbacks *callbacks, void *userdata, int stackSize)
-      : callbacks(callbacks), userdata(userdata), stackSize(stackSize) {
+      : callbacks(callbacks), userdata(userdata),
+        stackEnd(stack() + stackSize) {
     reset();
   }
 
@@ -91,7 +93,7 @@ struct Parser3 {
     --stackPtr;
   }
   [[nodiscard]] WeaselJsonStatus push(std::initializer_list<Symbol> symbols) {
-    if (stackPtr >= stack() + stackSize - symbols.size()) [[unlikely]] {
+    if (stackEnd - stackPtr < ptrdiff_t(symbols.size())) [[unlikely]] {
       return WeaselJson_OVERFLOW;
     }
     for (int i = symbols.size() - 1; i >= 0; --i) {
@@ -121,10 +123,10 @@ struct Parser3 {
   WeaselJsonCallbacks const *const callbacks;
   void *const userdata;
   Symbol *stackPtr;
+  Symbol *const stackEnd;
   uint32_t utf8Codepoint;
   uint32_t utf16Surrogate;
   uint32_t minCodepoint;
-  int const stackSize;
   NumDfa numDfa;
   Utf8Dfa strDfa;
 };