diff --git a/qwt/src/qwt_date.cpp b/qwt/src/qwt_date.cpp
index 0cf5ca0d2..741eb8663 100644
--- a/qwt/src/qwt_date.cpp
+++ b/qwt/src/qwt_date.cpp
@@ -313,7 +313,7 @@ QDateTime QwtDate::ceil( const QDateTime &dateTime, IntervalType intervalType )
         {
             qwtFloorTime( QwtDate::Second, dt );
             if ( dt < dateTime )
-                dt.addSecs( 1 );
+                dt = dt.addSecs( 1 );
 
             break;
         }
@@ -321,7 +321,7 @@ QDateTime QwtDate::ceil( const QDateTime &dateTime, IntervalType intervalType )
         {
             qwtFloorTime( QwtDate::Minute, dt );
             if ( dt < dateTime )
-                dt.addSecs( 60 );
+                dt = dt.addSecs( 60 );
 
             break;
         }
@@ -329,7 +329,7 @@ QDateTime QwtDate::ceil( const QDateTime &dateTime, IntervalType intervalType )
         {
             qwtFloorTime( QwtDate::Hour, dt );
             if ( dt < dateTime )
-                dt.addSecs( 3600 );
+                dt = dt.addSecs( 3600 );
 
             break;
         }
@@ -362,7 +362,7 @@ QDateTime QwtDate::ceil( const QDateTime &dateTime, IntervalType intervalType )
                 dateTime.date().month() ) );
 
             if ( dt < dateTime )
-                dt.addMonths( 1 );
+                dt = dt.addMonths( 1 );
 
             break;
         }