diff --git a/libs/qwt/qwt_plot_curve.cpp b/libs/qwt/qwt_plot_curve.cpp
index 140cc5996ad82260e7b75f11cca801e44e3d1778..96d6e2a190f9f3eba4a12c8b9548815c9183d04b 100644
--- a/libs/qwt/qwt_plot_curve.cpp
+++ b/libs/qwt/qwt_plot_curve.cpp
@@ -349,7 +349,7 @@ void QwtPlotCurve::drawSeries( QPainter *painter,
     const QwtScaleMap &xMap, const QwtScaleMap &yMap,
     const QRectF &canvasRect, int from, int to ) const
 {
-    const size_t numSamples = dataSize();
+    const int numSamples = static_cast<int>(dataSize());
 
     if ( !painter || numSamples <= 0 )
         return;
@@ -405,7 +405,7 @@ void QwtPlotCurve::drawCurve( QPainter *painter, int style,
                 // we always need the complete
                 // curve for fitting
                 from = 0;
-                to = dataSize() - 1;
+                to = static_cast<int>(dataSize()) - 1;
             }
             drawLines( painter, xMap, yMap, canvasRect, from, to );
             break;
diff --git a/libs/qwt/qwt_point_data.cpp b/libs/qwt/qwt_point_data.cpp
index d4eeaaabb32490634dd2d19a44a2659039a0ce14..4743d179c71c57ad483478609a6657f66c2fc9e0 100644
--- a/libs/qwt/qwt_point_data.cpp
+++ b/libs/qwt/qwt_point_data.cpp
@@ -37,10 +37,10 @@ QwtPointArrayData::QwtPointArrayData(
 QwtPointArrayData::QwtPointArrayData( const double *x,
         const double *y, size_t size )
 {
-    d_x.resize( size );
+    d_x.resize( static_cast<int>(size) );
     ::memcpy( d_x.data(), x, size * sizeof( double ) );
 
-    d_y.resize( size );
+    d_y.resize(static_cast<int>(size));
     ::memcpy( d_y.data(), y, size * sizeof( double ) );
 }
 
@@ -273,7 +273,7 @@ QPointF QwtSyntheticPointData::sample( size_t index ) const
     if ( index >= d_size )
         return QPointF( 0, 0 );
 
-    const double xValue = x( index );
+    const double xValue = x( static_cast<uint>(index) );
     const double yValue = y( xValue );
 
     return QPointF( xValue, yValue );
diff --git a/libs/qwt/qwt_series_data.cpp b/libs/qwt/qwt_series_data.cpp
index 319af41ff955a5089c49c74220b6dad6d6248003..f5c7618e031f6e0d9764b79d923733be393de039 100644
--- a/libs/qwt/qwt_series_data.cpp
+++ b/libs/qwt/qwt_series_data.cpp
@@ -78,7 +78,7 @@ QRectF qwtBoundingRectT(
         from = 0;
 
     if ( to < 0 )
-        to = series.size() - 1;
+        to = static_cast<int>(series.size()) - 1;
 
     if ( to < from )
         return boundingRect;