--- a/ext/gd/libgd/gdkanji.c
+++ b/ext/gd/libgd/gdkanji.c
@@ -9,6 +9,11 @@
 #include "gdhelpers.h"
 
 #include <stdarg.h>
+
+/* force usage of internal conversation routine */
+#undef HAVE_ICONV_H
+#undef HAVE_ICONV
+
 #if defined(HAVE_ICONV_H) || defined(HAVE_ICONV)
 #include <iconv.h>
 #ifdef HAVE_ERRNO_H
