diff --git a/src/util/std_expr.cpp b/src/util/std_expr.cpp
index 88608f650b7..ac7139113df 100644
--- a/src/util/std_expr.cpp
+++ b/src/util/std_expr.cpp
@@ -197,3 +197,16 @@ struct_exprt::component(const irep_idt &name, const namespacet &ns) const
 {
   return ::component(*this, name, ns);
 }
+
+const exprt &object_descriptor_exprt::root_object() const
+{
+  const exprt *p = &object();
+
+  while(p->id() == ID_member || p->id() == ID_index)
+  {
+    assert(!p->operands().empty());
+    p = &p->op0();
+  }
+
+  return *p;
+}
diff --git a/src/util/std_expr.h b/src/util/std_expr.h
index 97861252881..b1cf4bacb57 100644
--- a/src/util/std_expr.h
+++ b/src/util/std_expr.h
@@ -1966,18 +1966,7 @@ class object_descriptor_exprt:public binary_exprt
     return op0();
   }
 
-  const exprt &root_object() const
-  {
-    const exprt *p=&object();
-
-    while(p->id()==ID_member || p->id()==ID_index)
-    {
-      assert(!p->operands().empty());
-      p=&p->op0();
-    }
-
-    return *p;
-  }
+  const exprt &root_object() const;
 
   exprt &offset()
   {