--- source/common/ucnvmbcs.c
+++ source/common/ucnvmbcs.c
@@ -56,6 +56,11 @@
 #include "cmemory.h"
 #include "cstring.h"
 
+/* si_value is defined as a macro in some POSIX implementations' standard headers. */
+#ifdef si_value
+#undef si_value
+#endif
+
 /* control optimizations according to the platform */
 #define MBCS_UNROLL_SINGLE_TO_BMP 1
 #define MBCS_UNROLL_SINGLE_FROM_BMP 0