diff --git a/kstyle/breeze.h b/kstyle/breeze.h
--- a/kstyle/breeze.h
+++ b/kstyle/breeze.h
@@ -185,6 +185,9 @@
 
         // The standard pen stroke width for shadows.
         static constexpr int Shadow = 1;
+        
+        // A value for pen width arguments to make it clear that there is no pen stroke
+        static constexpr int NoPen = 0;
     }
     
     //* animation mode
diff --git a/kstyle/breezehelper.h b/kstyle/breezehelper.h
--- a/kstyle/breezehelper.h
+++ b/kstyle/breezehelper.h
@@ -311,8 +311,12 @@
         //@}
 
         //* frame radius
-        qreal frameRadius( qreal bias = 0 ) const
-        { return qMax( qreal( Metrics::Frame_FrameRadius ) - 0.5 + bias, 0.0 ); }
+        constexpr qreal frameRadius( const int penWidth = PenWidth::NoPen, const qreal bias = 0 ) const
+        { return qMax( Metrics::Frame_FrameRadius - (0.5 * penWidth) + bias, 0.0 ); }
+        
+        //* frame radius with new pen width
+        constexpr qreal frameRadiusForNewPenWidth( const qreal oldRadius, const int penWidth ) const
+        { return qMax( oldRadius - (0.5 * penWidth), 0.0 ); }
         
         //* return a QRectF with the appropriate size for a rectangle with a pen stroke
         QRectF strokedRect( const QRectF &rect, const int penWidth = PenWidth::Frame ) const;
diff --git a/kstyle/breezehelper.cpp b/kstyle/breezehelper.cpp
--- a/kstyle/breezehelper.cpp
+++ b/kstyle/breezehelper.cpp
@@ -461,7 +461,7 @@
 
             QRectF copy( strokedRect( rect ) );
 
-            const qreal radius( frameRadius( -1.0 ) );
+            const qreal radius( frameRadius( PenWidth::Frame, -1 ) );
             if( !(sides&SideTop) ) copy.adjust( 0, -radius, 0, 0 );
             if( !(sides&SideBottom) ) copy.adjust( 0, 0, 0, radius );
             if( !(sides&SideLeft) ) copy.adjust( -radius, 0, 0, 0 );
@@ -500,15 +500,15 @@
         painter->setRenderHint( QPainter::Antialiasing );
 
         QRectF frameRect( rect.adjusted( 1, 1, -1, -1 ) );
-        qreal radius( frameRadius() );
+        qreal radius( frameRadius( PenWidth::NoPen, -1 ) );
 
         // set pen
         if( outline.isValid() )
         {
 
             painter->setPen( outline );
             frameRect = strokedRect( frameRect );
-            radius = qMax( radius - 1, qreal( 0.0 ) );
+            radius = frameRadiusForNewPenWidth( radius, PenWidth::Frame );
 
         } else {
 
@@ -561,7 +561,7 @@
 
             case AllSides:
             {
-                const qreal radius( frameRadius( -1.0 ) );
+                const qreal radius( frameRadius( PenWidth::Frame, -1 ) );
                 painter->drawRoundedRect( frameRect, radius, radius );
                 break;
             }
@@ -586,15 +586,15 @@
 
             painter->setRenderHint( QPainter::Antialiasing );
             QRectF frameRect( rect );
-            qreal radius( frameRadius() );
+            qreal radius( frameRadius( PenWidth::NoPen, -1 ) );
 
             // set pen
             if( outline.isValid() )
             {
 
                 painter->setPen( outline );
                 frameRect = strokedRect( frameRect );
-                radius = qMax( radius - 1, qreal( 0.0 ) );
+                radius = frameRadiusForNewPenWidth( radius, PenWidth::Frame );
 
             } else painter->setPen( Qt::NoPen );
 
@@ -632,7 +632,7 @@
         // copy rect
         QRectF frameRect( rect );
         frameRect.adjust( 1, 1, -1, -1 );
-        qreal radius( frameRadius() );
+        qreal radius( frameRadius( PenWidth::NoPen, -1 ) );
 
         // shadow
         if( sunken ) {
@@ -654,7 +654,7 @@
             painter->setPen( QPen( QBrush( gradient ), 1.0 ) );
 
             frameRect = strokedRect( frameRect );
-            radius = qMax( radius - 1, qreal( 0.0 ) );
+            radius = frameRadiusForNewPenWidth( radius, PenWidth::Frame );
 
         } else painter->setPen( Qt::NoPen );
 
@@ -691,16 +691,16 @@
         if( sunken )
         {
 
-            const qreal radius( frameRadius() );
+            const qreal radius( frameRadius( PenWidth::NoPen ) );
 
             painter->setPen( Qt::NoPen );
             painter->setBrush( color );
 
             painter->drawRoundedRect( baseRect, radius, radius );
 
         } else {
 
-            const qreal radius( frameRadius(-0.5) );
+            const qreal radius( frameRadius( PenWidth::Frame ) );
 
             painter->setPen( color );
             painter->setBrush( Qt::NoBrush );
@@ -720,7 +720,7 @@
         if( !outline.isValid() ) return;
 
         // round radius
-        const qreal radius( frameRadius() );
+        const qreal radius( frameRadius( PenWidth::Frame ) );
         const QSizeF cornerSize( 2*radius, 2*radius );
 
         // if rect - tabwidth is even, need to increase tabWidth by 1 unit
@@ -761,15 +761,15 @@
         painter->setRenderHint( QPainter::Antialiasing );
 
         QRectF frameRect( rect.adjusted( 1, 1, -1, -1 ) );
-        qreal radius( frameRadius() );
+        qreal radius( frameRadius( PenWidth::NoPen, -1 ) );
 
         // set pen
         if( outline.isValid() )
         {
 
             painter->setPen( outline );
             frameRect = strokedRect( frameRect );
-            radius = qMax( radius-1, qreal( 0.0 ) );
+            radius = frameRadiusForNewPenWidth( radius, PenWidth::Frame );
 
         } else painter->setPen( Qt::NoPen );
 
@@ -858,7 +858,7 @@
         // copy rect and radius
         QRectF frameRect( rect );
         frameRect.adjust( 2, 2, -2, -2 );
-        qreal radius( frameRadius() );
+        qreal radius( frameRadius( PenWidth::NoPen, -1 ) );
 
         // shadow
         if( sunken )
@@ -878,7 +878,7 @@
             painter->setPen( QPen( color, PenWidth::Frame ) );
             painter->setBrush( Qt::NoBrush );
 
-            radius = qMax( radius-1, qreal( 0.0 ) );
+            radius = frameRadiusForNewPenWidth( radius, PenWidth::Frame );
             const QRectF contentRect( strokedRect( frameRect ) );
             painter->drawRoundedRect( contentRect, radius, radius );
 
@@ -1263,15 +1263,15 @@
         painter->setRenderHint( QPainter::Antialiasing, true );
 
         QRectF frameRect( rect );
-        qreal radius( frameRadius() );
+        qreal radius( frameRadius( PenWidth::NoPen, -1 ) );
 
         // pen
         if( outline.isValid() )
         {
 
             painter->setPen( outline );
             frameRect = strokedRect( frameRect );
-            radius = qMax( radius-1, qreal( 0.0 ) );
+            radius = frameRadiusForNewPenWidth( radius, PenWidth::Frame );
 
         } else painter->setPen( Qt::NoPen );