diff --git a/gcc/config/mips/iris3.h b/gcc/config/mips/iris3.h
index a0d3f2f164a..5358c795e31 100644
--- a/gcc/config/mips/iris3.h
+++ b/gcc/config/mips/iris3.h
@@ -84,7 +84,11 @@ the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
 
 #define NO_DOLLAR_IN_LABEL 1
 
-/* Specify size_t types.  */
+
+/* Specify size_t, ptrdiff_t, and wchar_t types.  */
 #define SIZE_TYPE	"unsigned int"
+#define PTRDIFF_TYPE	"int"
+#define WCHAR_TYPE	"unsigned char"
+#define WCHAR_TYPE_SIZE BITS_PER_UNIT
 
 #include "mips.h"