diff --git a/AK/String.cpp b/AK/String.cpp
index 66c01a21499..c5e6f7965c6 100644
--- a/AK/String.cpp
+++ b/AK/String.cpp
@@ -179,7 +179,8 @@ Optional<T> String::to_uint(TrimWhitespace trim_whitespace) const
 template Optional<u8> String::to_uint(TrimWhitespace) const;
 template Optional<u16> String::to_uint(TrimWhitespace) const;
 template Optional<u32> String::to_uint(TrimWhitespace) const;
-template Optional<u64> String::to_uint(TrimWhitespace) const;
+template Optional<unsigned long> String::to_uint(TrimWhitespace) const;
+template Optional<unsigned long long> String::to_uint(TrimWhitespace) const;
 
 bool String::starts_with(StringView str, CaseSensitivity case_sensitivity) const
 {