diff --git a/src/OpenFOAM/interpolations/interpolateSplineXY/interpolateSplineXY.C b/src/OpenFOAM/interpolations/interpolateSplineXY/interpolateSplineXY.C
index a322ff52affbf96377241d8012dc73f67ddc0f6a..65e9318ab30f99fb7baf62d2061246889540b890 100644
--- a/src/OpenFOAM/interpolations/interpolateSplineXY/interpolateSplineXY.C
+++ b/src/OpenFOAM/interpolations/interpolateSplineXY/interpolateSplineXY.C
@@ -6,6 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011 OpenFOAM Foundation
+    Copyright (C) 2024 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -60,11 +61,11 @@ Type Foam::interpolateSplineXY
     label n = xOld.size();
 
     // early exit if out of bounds or only one value
-    if (n == 1 || x < xOld[0])
+    if (n == 1 || x <= xOld[0])
     {
         return yOld[0];
     }
-    if (x > xOld[n - 1])
+    if (x >= xOld[n - 1])
     {
         return yOld[n - 1];
     }