diff --git a/src/OpenFOAM/meshes/boundBox/boundBoxI.H b/src/OpenFOAM/meshes/boundBox/boundBoxI.H
index b762840bc2..a71dba711a 100644
--- a/src/OpenFOAM/meshes/boundBox/boundBoxI.H
+++ b/src/OpenFOAM/meshes/boundBox/boundBoxI.H
@@ -159,7 +159,7 @@ inline Foam::scalar Foam::boundBox::avgDim() const
 }
 
 
-Foam::label Foam::boundBox::nDim() const
+inline Foam::label Foam::boundBox::nDim() const
 {
     label ngood = 0;