diff --git a/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H b/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H
index 564742d491..c3b09850f9 100644
--- a/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H
+++ b/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H
@@ -162,7 +162,7 @@ inline void Foam::FixedList<T, Size>::checkIndex(const label i) const
             << "attempt to access element from zero-sized list"
             << abort(FatalError);
     }
-    else if (i < 0 || i >= Size)
+    else if (i < 0 || i >= label(Size))
     {
         FatalErrorIn("FixedList<T, Size>::checkIndex(const label)")
             << "index " << i << " out of range 0 ... " << (Size-1)