diff --git a/lib/base/convert.cpp b/lib/base/convert.cpp
index 3c60e1b44..19d3e44e4 100644
--- a/lib/base/convert.cpp
+++ b/lib/base/convert.cpp
@@ -3,6 +3,7 @@
 #include "base/convert.hpp"
 #include "base/datetime.hpp"
 #include <boost/lexical_cast.hpp>
+#include <iomanip>
 
 using namespace icinga;
 
@@ -21,10 +22,10 @@ String Convert::ToString(double val)
 	double integral;
 	double fractional = std::modf(val, &integral);
 
-	if (fractional == 0)
-		return Convert::ToString(static_cast<long long>(val));
-
 	std::ostringstream msgbuf;
+	if (fractional == 0) {
+		msgbuf << std::setprecision(0);
+	}
 	msgbuf << std::fixed << val;
 	return msgbuf.str();
 }
diff --git a/test/base-convert.cpp b/test/base-convert.cpp
index 17805ea5c..bc7c61be8 100644
--- a/test/base-convert.cpp
+++ b/test/base-convert.cpp
@@ -33,12 +33,14 @@ BOOST_AUTO_TEST_CASE(tostring)
 	BOOST_CHECK(Convert::ToString(7) == "7");
 	BOOST_CHECK(Convert::ToString(7.5) == "7.500000");
 	BOOST_CHECK(Convert::ToString("hello") == "hello");
+	BOOST_CHECK(Convert::ToString(18446744073709551616.0) == "18446744073709551616"); // pow(2, 64)
 
 	String str = "hello";
 	BOOST_CHECK(Convert::ToString(str) == "hello");
 
 	BOOST_CHECK(Convert::ToString(Value(7)) == "7");
 	BOOST_CHECK(Convert::ToString(Value(7.5)) == "7.500000");
+	BOOST_CHECK(Convert::ToString(Value(18446744073709551616.0)) == "18446744073709551616"); // pow(2, 64)
 	BOOST_CHECK(Convert::ToString(Value("hello")) == "hello");
 	BOOST_CHECK(Convert::ToString(Value("hello hello")) == "hello hello");
 }