diff --git a/ThirdParty/Ert/lib/ecl/smspec_node.cpp b/ThirdParty/Ert/lib/ecl/smspec_node.cpp
index 786dd87430..98bf35b597 100644
--- a/ThirdParty/Ert/lib/ecl/smspec_node.cpp
+++ b/ThirdParty/Ert/lib/ecl/smspec_node.cpp
@@ -188,7 +188,7 @@ std::string smspec_alloc_completion_ijk_key( const char * join_string , const st
                                join_string ,
                                i , j , k );
   else
-    return NULL;
+    return std::string();
 }
 
 
@@ -202,7 +202,7 @@ std::string smspec_alloc_completion_num_key( const char * join_string , const st
                               join_string ,
                               num );
   else
-    return NULL;
+      return std::string();
 }
 
 /*
@@ -265,7 +265,7 @@ std::string smspec_alloc_segment_key( const char * join_string , const std::stri
                               join_string ,
                               num );
   else
-    return NULL;
+    return std::string();
 }
 
 
@@ -278,7 +278,7 @@ std::string smspec_alloc_local_well_key( const char * join_string , const std::s
                                join_string ,
                                wgname.c_str());
   else
-    return NULL;
+    return std::string();
 }
 
 std::string smspec_alloc_local_completion_key( const char * join_string, const std::string& keyword , const std::string& lgr_name , const std::string& wgname , int i , int j , int k) {
@@ -292,7 +292,7 @@ std::string smspec_alloc_local_completion_key( const char * join_string, const s
                               join_string ,
                               i,j,k);
   else
-    return NULL;
+    return std::string();
 }
 
 /*****************************************************************/