diff --git a/include/ecrt.h b/include/ecrt.h
index c14af99648c74b2e022bae9842c3ea226a8ea9c4..590a88b1bc3fc9a484d70903ace25d7e7236e4fb 100644
--- a/include/ecrt.h
+++ b/include/ecrt.h
@@ -785,7 +785,7 @@ int ecrt_domain_reg_pdo_entry_list(
  * \return Size of the process data image.
  */
 size_t ecrt_domain_size(
-        ec_domain_t *domain /**< Domain. */
+        const ec_domain_t *domain /**< Domain. */
         );
 
 #ifdef __KERNEL__
diff --git a/lib/domain.c b/lib/domain.c
index 4711b118c40af01c4cb9d35e88ce9dd6abfb7d8c..ea3bb5ac564624e37e1ed34e2e69f2abc7812a8f 100644
--- a/lib/domain.c
+++ b/lib/domain.c
@@ -66,13 +66,6 @@ int ecrt_domain_reg_pdo_entry_list(ec_domain_t *domain,
 
 /*****************************************************************************/
 
-size_t ecrt_domain_size(ec_domain_t *domain)
-{
-	return 0;
-}
-
-/*****************************************************************************/
-
 uint8_t *ecrt_domain_data(ec_domain_t *domain)
 {
     return 0;
diff --git a/master/domain.c b/master/domain.c
index 1e0a3aef100106bc60d804fa6876199d51af234c..0b8818c7e049f3bfa04955e3575dd233012eb087 100644
--- a/master/domain.c
+++ b/master/domain.c
@@ -344,7 +344,7 @@ int ecrt_domain_reg_pdo_entry_list(ec_domain_t *domain,
 
 /*****************************************************************************/
 
-size_t ecrt_domain_size(ec_domain_t *domain)
+size_t ecrt_domain_size(const ec_domain_t *domain)
 {
     return domain->data_size;
 }