diff --git a/CHANGELOG.md b/CHANGELOG.md
index 594c1069..9b6e08a8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,8 @@ FlatLaf Change Log
   #1068)
 - Popup: Fixed scrolling popup painting issue on Windows 10 when a glass pane is
   visible and frame is maximized. (issue #1071)
+- Slider: Styling `thumbSize` or `focusWidth` did not update slider size/layout.
+  (PR #1074)
 - ToolBar: Grip disappeared when switching between Look and Feels. (issue #1075)
 - Extras:
   - UI defaults inspector: Fixed NPE if color of `FlatLineBorder` is null. Also
diff --git a/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatSliderUI.java b/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatSliderUI.java
index 7870f054..a830fdf3 100644
--- a/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatSliderUI.java
+++ b/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatSliderUI.java
@@ -227,7 +227,13 @@ public class FlatSliderUI
 
 	/** @since 2 */
 	protected void applyStyle( Object style ) {
+		Dimension oldThumbSize = thumbSize;
+		int oldFocusWidth = focusWidth;
+
 		oldStyleValues = FlatStylingSupport.parseAndApply( oldStyleValues, style, this::applyStyleProperty );
+
+		if( !thumbSize.equals( oldThumbSize ) || focusWidth != oldFocusWidth )
+			calculateGeometry();
 	}
 
 	/** @since 2 */