-#if defined(DLLFNAME_POSTFIX) && !defined(PRIVATEBUILD) && !defined(SPECIALBUILD)
-# error PRIVATEBUILD or SPECIALBUILD must be defined as a string describing the type of change brought to the standard library
-#endif /* defined(DLLFNAME_POSTFIX)... */
+/* Support deprecated PRIVATEBUILD macro */
+#if defined(PRIVATEBUILD) && !defined(PNG_USER_PRIVATEBUILD)
+# define PNG_USER_PRIVATEBUILD PRIVATEBUILD
+#endif
+
+#if defined(PNG_USER_DLLFNAME_POSTFIX) && !defined(PNG_USER_PRIVATEBUILD)
+# error "PNG_USER_PRIVATEBUILD must be defined as a string describing the\
+ custom changes made to the library."
+#endif
+
+/* Prioritize PNG_USER_x over PNG_LIBPNG_x */
+#ifdef PNG_USER_DLLFNAME_POSTFIX
+# undef PNG_LIBPNG_DLLFNAME_POSTFIX
+# define PNG_LIBPNG_DLLFNAME_POSTFIX PNG_USER_DLLFNAME_POSTFIX
+#endif