diff --git a/tune/common.c b/tune/common.c
index 9fefb0d..545abfa 100644
--- a/tune/common.c
+++ b/tune/common.c
@@ -1722,6 +1722,11 @@ speed_mpn_gcd_1N (struct speed_params *s)
   SPEED_ROUTINE_MPN_GCD_1N (mpn_gcd_1);
 }
 
+double
+speed_mpz_nextprime (struct speed_params *s)
+{
+  SPEED_ROUTINE_MPZ_NEXTPRIME (mpz_nextprime);
+}
 
 double
 speed_mpz_jacobi (struct speed_params *s)
diff --git a/tune/speed.c b/tune/speed.c
index 82e9c1a..588b7eb 100644
--- a/tune/speed.c
+++ b/tune/speed.c
@@ -307,6 +307,9 @@ const struct routine_t {
 #if 0
   { "mpn_gcdext_lehmer",     speed_mpn_gcdext_lehmer     },
 #endif
+
+  { "mpz_nextprime",     speed_mpz_nextprime        },
+
   { "mpz_jacobi",        speed_mpz_jacobi           },
   { "mpn_jacobi_base",   speed_mpn_jacobi_base      },
   { "mpn_jacobi_base_1", speed_mpn_jacobi_base_1    },
diff --git a/tune/speed.h b/tune/speed.h
index 6ea000b..2cf9dde 100644
--- a/tune/speed.h
+++ b/tune/speed.h
@@ -396,6 +396,7 @@ double speed_mpz_fib_ui (struct speed_params *);
 double speed_mpz_fib2_ui (struct speed_params *);
 double speed_mpz_init_clear (struct speed_params *);
 double speed_mpz_init_realloc_clear (struct speed_params *);
+double speed_mpz_nextprime (struct speed_params *);
 double speed_mpz_jacobi (struct speed_params *);
 double speed_mpz_lucnum_ui (struct speed_params *);
 double speed_mpz_lucnum2_ui (struct speed_params *);
@@ -3099,6 +3100,47 @@ int speed_routine_count_zeros_setup (struct speed_params *, mp_ptr, int, int);
     return t;								\
   }
 
+/* Calculate nextprime(n) for random n of s->size bits (not limbs). */
+#define SPEED_ROUTINE_MPZ_NEXTPRIME(function)				\
+  {									\
+    unsigned  i, j;							\
+    mpz_t     wp, n;							\
+    double    t;							\
+									\
+    SPEED_RESTRICT_COND (s->size >= 10);				\
+									\
+    mpz_init (wp);							\
+    mpz_init_set_n (n, s->xp, s->size);					\
+    /* limit to s->size bits, as this function is very slow */		\
+    mpz_tdiv_r_2exp (n, n, s->size);					\
+    /* set high bits so operand and result are genaral s->size bits */	\
+    mpz_setbit (n, s->size - 1);					\
+    mpz_clrbit (n, s->size - 2);					\
+									\
+    speed_starttime ();							\
+    i = s->reps;							\
+    do									\
+      {									\
+        /* nextprime timing is variable, so average over many calls */	\
+        j = SPEED_BLOCK_SIZE - 1;					\
+        /* starts on random, after measures prime to next prime */	\
+        function (wp, n);						\
+        do								\
+          {								\
+            function (wp, wp);						\
+          }								\
+        while (--j != 0);						\
+      }									\
+    while (--i != 0);							\
+    t = speed_endtime ();						\
+									\
+    mpz_clear (wp);							\
+    mpz_clear (n);							\
+									\
+    s->time_divisor = SPEED_BLOCK_SIZE;					\
+    return t;								\
+  }
+
 #define SPEED_ROUTINE_MPZ_JACOBI(function)				\
   {									\
     mpz_t     a, b;							\