diff --git a/lib/mpi/longlong.h b/lib/mpi/longlong.h
index 57fd45ab7af1..08c60d10747f 100644
--- a/lib/mpi/longlong.h
+++ b/lib/mpi/longlong.h
@@ -671,7 +671,23 @@ do {						\
 	**************  MIPS/64  **************
 	***************************************/
 #if (defined(__mips) && __mips >= 3) && W_TYPE_SIZE == 64
-#if (__GNUC__ >= 5) || (__GNUC__ >= 4 && __GNUC_MINOR__ >= 4)
+#if defined(__mips_isa_rev) && __mips_isa_rev >= 6
+/*
+ * GCC ends up emitting a __multi3 intrinsic call for MIPS64r6 with the plain C
+ * code below, so we special case MIPS64r6 until the compiler can do better.
+ */
+#define umul_ppmm(w1, w0, u, v)						\
+do {									\
+	__asm__ ("dmulu %0,%1,%2"					\
+		 : "=d" ((UDItype)(w0))					\
+		 : "d" ((UDItype)(u)),					\
+		   "d" ((UDItype)(v)));					\
+	__asm__ ("dmuhu %0,%1,%2"					\
+		 : "=d" ((UDItype)(w1))					\
+		 : "d" ((UDItype)(u)),					\
+		   "d" ((UDItype)(v)));					\
+} while (0)
+#elif (__GNUC__ >= 5) || (__GNUC__ >= 4 && __GNUC_MINOR__ >= 4)
 #define umul_ppmm(w1, w0, u, v) \
 do {									\
 	typedef unsigned int __ll_UTItype __attribute__((mode(TI)));	\