diff --git a/src/Wt/WDate.C b/src/Wt/WDate.C
index 90cf95ae1..841c2c743 100644
--- a/src/Wt/WDate.C
+++ b/src/Wt/WDate.C
@@ -124,7 +124,10 @@ void WDate::setDate(int year, int month, int day)
 
 void WDate::setYmd(int y, int m, int d)
 {
-  ymd_ = (y << 16) | ((m & 0xFF) << 8) | (d & 0xFF);
+  ymd_ = static_cast<int>(
+      (static_cast<unsigned>(y) << 16) |
+      ((static_cast<unsigned>(m) & 0xFF) << 8) |
+       (static_cast<unsigned>(d) & 0xFF));
 }
 
 bool WDate::isLeapYear(int year)
diff --git a/src/Wt/WDate.h b/src/Wt/WDate.h
index 8b385ae86..10b345c65 100644
--- a/src/Wt/WDate.h
+++ b/src/Wt/WDate.h
@@ -162,7 +162,7 @@ class WT_API WDate
    *
    * \sa isNull(), WDate(int, int, int), setDate()
    */
-  bool isValid() const { return ymd_ > 1; }
+  bool isValid() const { return ymd_ != 0 && ymd_ != 1; }
 
   /*! \brief Returns the year.
    *
@@ -447,7 +447,7 @@ class WT_API WDate
   static RegExpInfo formatToRegExp(const WT_USTRING& format);
 
 private:
-  unsigned ymd_;
+  int ymd_;
 
   void setYmd(int year, int month, int day);