diff --git a/addons/addon-fit/src/FitAddon.ts b/addons/addon-fit/src/FitAddon.ts
index 3db988acd..fab52dfde 100644
--- a/addons/addon-fit/src/FitAddon.ts
+++ b/addons/addon-fit/src/FitAddon.ts
@@ -74,8 +74,8 @@ export class FitAddon implements ITerminalAddon, IFitApi {
       : (this._terminal.options.scrollbar?.width ?? ViewportConstants.DEFAULT_SCROLL_BAR_WIDTH));
 
     const parentElementStyle = _getComputedStyle(this._terminal.element.parentElement);
-    const parentElementHeight = parseInt(parentElementStyle.getPropertyValue('height'));
-    const parentElementWidth = Math.max(0, parseInt(parentElementStyle.getPropertyValue('width')));
+    const parentElementHeight = Math.max(0, parseInt(parentElementStyle.getPropertyValue('height'), 10) || 0);
+    const parentElementWidth = Math.max(0, parseInt(parentElementStyle.getPropertyValue('width'), 10) || 0);
     const elementStyle = _getComputedStyle(this._terminal.element);
     const elementPadding = {
       top: parseInt(elementStyle.getPropertyValue('padding-top')),