diff --git a/Source.Common/Platform.cs b/Source.Common/Platform.cs
index dcf28d2a..62a5d984 100644
--- a/Source.Common/Platform.cs
+++ b/Source.Common/Platform.cs
@@ -1,6 +1,7 @@
 using Source.Common;
 
 using System.Diagnostics;
+using System.Globalization;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
@@ -48,6 +49,13 @@ public static unsafe void DebugString(ReadOnlySpan<char> buf) {
 	}
 
 	public static void Initialize() {
+		// Source's data files (KeyValues, .res, .vmt, convar values) are always en-US formatted, so the
+		// process must not follow the user's locale - float.Parse("0.25") throws under fr-FR otherwise.
+		CultureInfo.DefaultThreadCurrentCulture = CultureInfo.InvariantCulture;
+		CultureInfo.DefaultThreadCurrentUICulture = CultureInfo.InvariantCulture;
+		Thread.CurrentThread.CurrentCulture = CultureInfo.InvariantCulture;
+		Thread.CurrentThread.CurrentUICulture = CultureInfo.InvariantCulture;
+
 		ThreadUtils.SetMainThread();
 	}
 }
diff --git a/Source.GUI.Controls/PropertySheet.cs b/Source.GUI.Controls/PropertySheet.cs
index d5b248a6..20bd76a3 100644
--- a/Source.GUI.Controls/PropertySheet.cs
+++ b/Source.GUI.Controls/PropertySheet.cs
@@ -2,6 +2,8 @@
 using Source.Common.GUI;
 using Source.Common.Input;
 
+using System.Globalization;
+
 namespace Source.GUI.Controls;
 
 class ContextLabel : Label
@@ -534,7 +536,7 @@ public override void ApplySchemeSettings(IScheme scheme) {
 			Border = scheme.GetBorder("RaisedBorder")!;
 
 		SetBorder(Border);
-		PageTransitionEffectTime = float.Parse(scheme.GetResourceString("PropertySheet.TransitionEffectTime"));
+		PageTransitionEffectTime = float.TryParse(scheme.GetResourceString("PropertySheet.TransitionEffectTime"), NumberStyles.Float, CultureInfo.InvariantCulture, out float transitionTime) ? transitionTime : 0;
 		TabFont = scheme.GetFont(SmallTabs ? "DefaultVerySmall" : "DefaultSmall")!;
 
 		if (TabKV != null)