diff --git a/src/pe_coupling/geometry/PeOverlapFraction.h b/src/pe_coupling/geometry/PeOverlapFraction.h
index 7193aae0a465b3915219602c145a45e567f34654..f8bae664e9762df51ca602bdfe9398b2c18c6433 100644
--- a/src/pe_coupling/geometry/PeOverlapFraction.h
+++ b/src/pe_coupling/geometry/PeOverlapFraction.h
@@ -34,8 +34,8 @@ namespace walberla {
 namespace pe_coupling{
 
 
-real_t overlapFractionPe( const pe::RigidBody & peRigidBody, const Vector3<real_t> & cellMidpoint,
-                          const Vector3<real_t> & dx, uint_t maxDepth=4 )
+inline real_t overlapFractionPe( const pe::RigidBody & peRigidBody, const Vector3<real_t> & cellMidpoint,
+                                 const Vector3<real_t> & dx, uint_t maxDepth=4 )
 {
    if( peRigidBody.getTypeID() == pe::Sphere::getStaticTypeID() || peRigidBody.getTypeID() == pe::Squirmer::getStaticTypeID() )
    {