diff --git a/Userland/Libraries/LibC/limits.h b/Userland/Libraries/LibC/limits.h
index 58a980bde87..f7365e6e61d 100644
--- a/Userland/Libraries/LibC/limits.h
+++ b/Userland/Libraries/LibC/limits.h
@@ -41,10 +41,18 @@
 
 #define USHRT_MAX 65535
 
-#define LONG_MAX 2147483647L
+#ifdef __x86_64__
+#    define LONG_MAX 9223372036854775807L
+#else
+#    define LONG_MAX 2147483647L
+#endif
 #define LONG_MIN (-LONG_MAX - 1L)
 
-#define ULONG_MAX 4294967295UL
+#ifdef __x86_64__
+#    define ULONG_MAX 18446744073709551615UL
+#else
+#    define ULONG_MAX 4294967295UL
+#endif
 
 #define LONG_LONG_MAX 9223372036854775807LL
 #define LONG_LONG_MIN (-LONG_LONG_MAX - 1LL)