diff --git a/libclingo-lpx/src/number_flint.hh b/libclingo-lpx/src/number_flint.hh
index 74a761f..77ba3f2 100644
--- a/libclingo-lpx/src/number_flint.hh
+++ b/libclingo-lpx/src/number_flint.hh
@@ -7,8 +7,10 @@
 
 #include <ios>
 #include <iostream>
+#include <limits>
 #include <memory>
 #include <new>
+#include <optional>
 #include <stdexcept>
 #include <string>
 
diff --git a/libclingo-lpx/src/number_imath.hh b/libclingo-lpx/src/number_imath.hh
index 3daade0..7ea37da 100644
--- a/libclingo-lpx/src/number_imath.hh
+++ b/libclingo-lpx/src/number_imath.hh
@@ -7,8 +7,10 @@
 
 #include <ios>
 #include <iostream>
+#include <limits>
 #include <memory>
 #include <new>
+#include <optional>
 #include <stdexcept>
 #include <string>
 
@@ -253,7 +255,7 @@ inline auto Integer::neg() -> Integer & {
 }
 
 inline auto Integer::as_int() const -> std::optional<int> {
-    mp_small = res;
+    auto res = mp_small{};
     if (mp_int_to_int(&num_, &res) == MP_OK) {
         if (std::numeric_limits<int>::min() <= res && res <= std::numeric_limits<int>::max()) {
             return res;
diff --git a/libclingo-lpx/src/parsing.cc b/libclingo-lpx/src/parsing.cc
index 0068df4..dd1eb68 100644
--- a/libclingo-lpx/src/parsing.cc
+++ b/libclingo-lpx/src/parsing.cc
@@ -5,11 +5,11 @@
 
 #include <algorithm>
 #include <iterator>
-#include <map>
 #include <optional>
 #include <regex>
 #include <stdexcept>
 #include <unordered_map>
+#include <variant>
 
 namespace {