diff --git a/src/time/ISO8601.cxx b/src/time/ISO8601.cxx
index 514c8a23b..067e4c4ee 100644
--- a/src/time/ISO8601.cxx
+++ b/src/time/ISO8601.cxx
@@ -35,10 +35,9 @@
 #include "util/StringBuffer.hxx"
 
 #include <cassert>
+#include <cstdlib>
 #include <stdexcept>
 
-#include <stdlib.h>
-
 StringBuffer<64>
 FormatISO8601(const struct tm &tm) noexcept
 {
@@ -65,7 +64,7 @@ static std::pair<unsigned, unsigned>
 ParseTimeZoneOffsetRaw(const char *&s)
 {
 	char *endptr;
-	unsigned long value = strtoul(s, &endptr, 10);
+	unsigned long value = std::strtoul(s, &endptr, 10);
 	if (endptr == s + 4) {
 		s = endptr;
 		return std::make_pair(value / 100, value % 100);
@@ -75,7 +74,7 @@ ParseTimeZoneOffsetRaw(const char *&s)
 		unsigned hours = value, minutes = 0;
 		if (*s == ':') {
 			++s;
-			minutes = strtoul(s, &endptr, 10);
+			minutes = std::strtoul(s, &endptr, 10);
 			if (endptr != s + 2)
 				throw std::runtime_error("Failed to parse time zone offset");
 
diff --git a/src/time/ISO8601.hxx b/src/time/ISO8601.hxx
index eec40da69..ceb97bfee 100644
--- a/src/time/ISO8601.hxx
+++ b/src/time/ISO8601.hxx
@@ -36,9 +36,8 @@
 #include "util/Compiler.h"
 
 #include <chrono>
-#include <utility>
-
 #include <cstddef>
+#include <utility>
 
 struct tm;
 template<size_t CAPACITY> class StringBuffer;