diff --git a/sql/sql_class.cc b/sql/sql_class.cc
index 0a3d0fc56e0..326b8a3f16a 100644
--- a/sql/sql_class.cc
+++ b/sql/sql_class.cc
@@ -141,6 +141,17 @@ bool Key_part_spec::check_key_for_blob(const handler *file) const
 }
 
 
+bool Key_part_spec::check_key_length_for_blob() const
+{
+  if (!length)
+  {
+    my_error(ER_BLOB_KEY_WITHOUT_LENGTH, MYF(0), field_name.str);
+    return true;
+  }
+  return false;
+}
+
+
 bool Key_part_spec::init_multiple_key_for_blob(const handler *file)
 {
   if (check_key_for_blob(file))
diff --git a/sql/sql_class.h b/sql/sql_class.h
index ab7f06304c2..bad9a5796f8 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -290,15 +290,7 @@ public:
   Key_part_spec *clone(MEM_ROOT *mem_root) const
   { return new (mem_root) Key_part_spec(*this); }
   bool check_key_for_blob(const class handler *file) const;
-  bool check_key_length_for_blob() const
-  {
-    if (!length)
-    {
-      my_error(ER_BLOB_KEY_WITHOUT_LENGTH, MYF(0), field_name.str);
-      return true;
-    }
-    return false;
-  }
+  bool check_key_length_for_blob() const;
   bool check_primary_key_for_blob(const class handler *file) const
   {
     return check_key_for_blob(file) || check_key_length_for_blob();