diff --git a/src/declarativeimports/plasmacomponents3/ToolButton.qml b/src/declarativeimports/plasmacomponents3/ToolButton.qml
--- a/src/declarativeimports/plasmacomponents3/ToolButton.qml
+++ b/src/declarativeimports/plasmacomponents3/ToolButton.qml
@@ -28,6 +28,10 @@
 T.ToolButton {
     id: control
 
+    // Match default size of QWidgets ToolButton
+    icon.height: icon.source.length > 0 ? units.iconSizes.smallMedium : undefined
+    icon.width: icon.source.length > 0 ? units.iconSizes.smallMedium : undefined
+
     implicitWidth: Math.max(background.implicitWidth,
                             contentItem.implicitWidth + leftPadding + rightPadding)
     implicitHeight: Math.max(background.implicitHeight, contentItem.implicitHeight + topPadding + bottomPadding)