diff --git a/src/json.hpp b/src/json.hpp
index 6b4c92d5..72c3f28e 100644
--- a/src/json.hpp
+++ b/src/json.hpp
@@ -14,6 +14,7 @@ Licensed under the MIT License <http://opensource.org/licenses/MIT>.
 #include <algorithm>
 #include <array>
 #include <cassert>
+#include <cerrno>
 #include <ciso646>
 #include <cmath>
 #include <cstddef>
diff --git a/src/json.hpp.re2c b/src/json.hpp.re2c
index 6edc4ab1..a8b1b85c 100644
--- a/src/json.hpp.re2c
+++ b/src/json.hpp.re2c
@@ -14,6 +14,7 @@ Licensed under the MIT License <http://opensource.org/licenses/MIT>.
 #include <algorithm>
 #include <array>
 #include <cassert>
+#include <cerrno>
 #include <ciso646>
 #include <cmath>
 #include <cstddef>