diff --git a/include/wx/longlong.h b/include/wx/longlong.h
index 59dcd57c74..9b6553ea9a 100644
--- a/include/wx/longlong.h
+++ b/include/wx/longlong.h
@@ -410,6 +410,9 @@ public:
         return wx_truncate_cast(unsigned long, m_ll);
     }
 
+        // convert to double
+    double ToDouble() const { return wx_truncate_cast(double, m_ll); }
+
     // operations
         // addition
     wxULongLongNative operator+(const wxULongLongNative& ll) const
@@ -906,6 +909,9 @@ public:
         return (unsigned long)m_lo;
     }
 
+        // convert to double
+    double ToDouble() const;
+
     // operations
         // addition
     wxULongLongWx operator+(const wxULongLongWx& ll) const;
diff --git a/src/common/longlong.cpp b/src/common/longlong.cpp
index 360d087b3e..772ecc0b9a 100644
--- a/src/common/longlong.cpp
+++ b/src/common/longlong.cpp
@@ -194,6 +194,19 @@ double wxLongLongWx::ToDouble() const
     return d;
 }
 
+double wxULongLongWx::ToDouble() const
+{
+    unsigned double d = m_hi;
+    d *= 1.0 + (double)ULONG_MAX;
+    d += m_lo;
+
+#ifdef wxLONGLONG_TEST_MODE
+    wxASSERT( d == m_ll );
+#endif // wxLONGLONG_TEST_MODE
+
+    return d;
+}
+
 wxLongLongWx wxLongLongWx::operator<<(int shift) const
 {
     wxLongLongWx ll(*this);