4 files changed, 22 insertions, 2 deletions
diff --git a/src/corelib/json/qjson_p.h b/src/corelib/json/qjson_p.h
index 06885ad972..7d0162938d 100644
--- a/src/corelib/json/qjson_p.h
+++ b/src/corelib/json/qjson_p.h
@@ -60,8 +60,10 @@
 #include <qatomic.h>
 #include <qstring.h>
 #include <qendian.h>
+#include <qnumeric.h>
 
 #include <limits.h>
+#include <limits>
 
 QT_BEGIN_NAMESPACE
 
diff --git a/src/corelib/json/qjsonvalue.cpp b/src/corelib/json/qjsonvalue.cpp
index 3fbc811948..3aba6124b8 100644
--- a/src/corelib/json/qjsonvalue.cpp
+++ b/src/corelib/json/qjsonvalue.cpp
@@ -156,6 +156,18 @@ QJsonValue::QJsonValue(int n)
 }
 
 /*!
+    \overload
+    Creates a value of type Double, with value \a n.
+    NOTE: the integer limits for IEEE 754 double precision data is 2^53 (-9007199254740992 to +9007199254740992).
+    If you pass in values outside this range expect a loss of precision to occur.
+ */
+QJsonValue::QJsonValue(qint64 n)
+    : d(0), t(Double)
+{
+    this->dbl = n;
+}
+
+/*!
     Creates a value of type String, with value \a s.
  */
 QJsonValue::QJsonValue(const QString &s)
diff --git a/src/corelib/json/qjsonvalue.h b/src/corelib/json/qjsonvalue.h
index b8bdf55aa3..c8efab5d5f 100644
--- a/src/corelib/json/qjsonvalue.h
+++ b/src/corelib/json/qjsonvalue.h
@@ -79,6 +79,7 @@ public:
     QJsonValue(bool b);
     QJsonValue(double n);
     QJsonValue(int n);
+    QJsonValue(qint64 n);
     QJsonValue(const QString &s);
     QJsonValue(QLatin1String s);
     QJsonValue(const QJsonArray &a);
diff --git a/src/corelib/json/qjsonwriter.cpp b/src/corelib/json/qjsonwriter.cpp
index 3ac16c6fd1..8426b351f6 100644
--- a/src/corelib/json/qjsonwriter.cpp
+++ b/src/corelib/json/qjsonwriter.cpp
@@ -169,9 +169,14 @@ static void valueToJson(const QJsonPrivate::Base *b, const QJsonPrivate::Value &
     case QJsonValue::Bool:
         json += v.toBoolean() ? "true" : "false";
         break;
-    case QJsonValue::Double:
-        json += QByteArray::number(v.toDouble(b), 'g', 17);
+    case QJsonValue::Double: {
+        const double d = v.toDouble(b);
+        if (qIsFinite(d)) // +2 to format to ensure the expected precision
+            json += QByteArray::number(d, 'g', std::numeric_limits<double>::digits10 + 2); // ::digits10 is 15
+        else
+            json += "null"; // +INF || -INF || NaN (see RFC4627#section2.4)
         break;
+    }
     case QJsonValue::String:
         json += '"';
         json += escapedString(v.toString(b));