--- a/ucx/cx/collection.h	Sun Feb 11 15:44:33 2024 +0100
+++ b/ucx/cx/collection.h	Sun Feb 11 22:06:23 2024 +0100
@@ -30,7 +30,6 @@
  * \brief Common definitions for various collection implementations.
  * \author Mike Becker
  * \author Olaf Wintermann
- * \version 3.0
  * \copyright 2-Clause BSD License
  */
 
@@ -49,6 +48,8 @@
  */
 #define CX_STORE_POINTERS 0
 
+#ifndef CX_COMPARE_FUNC_DEFINED
+#define CX_COMPARE_FUNC_DEFINED
 /**
  * A comparator function comparing two collection elements.
  */
@@ -56,6 +57,7 @@
         void const *left,
         void const *right
 );
+#endif // CX_COMPARE_FUNC_DEFINED
 
 /**
  * Use this macro to declare common members for a collection structure.