diff --git a/src/mesh/blockMesh/gradingDescriptor/gradingDescriptor.C b/src/mesh/blockMesh/gradingDescriptor/gradingDescriptor.C
index ab04583dd8888526fe95d213cda401dce32afd5f..86785fa06b9d8e273433dc48b993567edb9a4164 100644
--- a/src/mesh/blockMesh/gradingDescriptor/gradingDescriptor.C
+++ b/src/mesh/blockMesh/gradingDescriptor/gradingDescriptor.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2015 OpenFOAM Foundation
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -129,6 +129,11 @@ Foam::Istream& Foam::operator>>(Istream& is, gradingDescriptor& gd)
         is.readEnd("gradingDescriptor");
     }
 
+    if (gd.expansionRatio_ < 0)
+    {
+        gd.expansionRatio_ = 1.0/(-gd.expansionRatio_);
+    }
+
     is.check(FUNCTION_NAME);
     return is;
 }