diff -r c9b02747cfc5 -r cc204fc56c9c src/szmul.c
--- a/src/szmul.c	Sat Nov 02 13:38:51 2024 +0100
+++ b/src/szmul.c	Sat Nov 02 13:48:53 2024 +0100
@@ -26,6 +26,9 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include "cx/common.h"
+
+#ifndef CX_SZMUL_BUILTIN
 int cx_szmul_impl(
         size_t a,
         size_t b,
@@ -44,3 +47,4 @@
         return 1;
     }
 }
+#endif // CX_SZMUL_BUILTIN