diff --git a/arb.h b/arb.h
index f4202c14..dad2fcbd 100644
--- a/arb.h
+++ b/arb.h
@@ -159,6 +159,7 @@ void arb_neg_round(arb_t x, const arb_t y, slong prec);
 void arb_abs(arb_t y, const arb_t x);
 
 void arb_sgn(arb_t res, const arb_t x);
+int arb_sgn_nonzero(const arb_t x);
 
 void _arb_digits_round_inplace(char * s, mp_bitcnt_t * shift, fmpz_t error, slong n, arf_rnd_t rnd);
 
diff --git a/arb/sgn_nonzero.c b/arb/sgn_nonzero.c
new file mode 100644
index 00000000..50645085
--- /dev/null
+++ b/arb/sgn_nonzero.c
@@ -0,0 +1,23 @@
+/*
+    Copyright (C) 2019 Fredrik Johansson
+
+    This file is part of Arb.
+
+    Arb is free software: you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License (LGPL) as published
+    by the Free Software Foundation; either version 2.1 of the License, or
+    (at your option) any later version.  See <http://www.gnu.org/licenses/>.
+*/
+
+#include "arb.h"
+
+int
+arb_sgn_nonzero(const arb_t x)
+{
+    if (arb_is_positive(x))
+        return 1;
+    else if (arb_is_negative(x))
+        return -1;
+    else
+        return 0;
+}
diff --git a/arb_calc/isolate_roots.c b/arb_calc/isolate_roots.c
index 07471530..c97fdf2f 100644
--- a/arb_calc/isolate_roots.c
+++ b/arb_calc/isolate_roots.c
@@ -15,18 +15,6 @@
 #define BLOCK_ISOLATED_ZERO 1
 #define BLOCK_UNKNOWN 2
 
-/* 0 means that it *could* be zero; otherwise +/- 1 */
-static __inline__ int
-_arb_sign(const arb_t t)
-{
-    if (arb_is_positive(t))
-        return 1;
-    else if (arb_is_negative(t))
-        return -1;
-    else
-        return 0;
-}
-
 static int
 check_block(arb_calc_func_t func, void * param, const arf_interval_t block,
     int asign, int bsign, slong prec)
@@ -175,11 +163,11 @@ arb_calc_isolate_roots(arf_interval_ptr * blocks, int ** flags,
 
     arb_set_arf(m, &block->a);
     func(v, m, param, 1, prec);
-    asign = _arb_sign(v);
+    asign = arb_sgn_nonzero(v);
 
     arb_set_arf(m, &block->b);
     func(v, m, param, 1, prec);
-    bsign = _arb_sign(v);
+    bsign = arb_sgn_nonzero(v);
 
     arb_clear(m);
     arb_clear(v);
diff --git a/arb_calc/refine_root_bisect.c b/arb_calc/refine_root_bisect.c
index 61e608b1..dcd6e0ff 100644
--- a/arb_calc/refine_root_bisect.c
+++ b/arb_calc/refine_root_bisect.c
@@ -13,18 +13,6 @@
 
 /* TODO: refactor/combine some of this code with isolate_roots.c */
 
-/* 0 means that it *could* be zero; otherwise +/- 1 */
-static __inline__ int
-_arb_sign(const arb_t t)
-{
-    if (arb_is_positive(t))
-        return 1;
-    else if (arb_is_negative(t))
-        return -1;
-    else
-        return 0;
-}
-
 int arb_calc_partition(arf_interval_t L, arf_interval_t R,
     arb_calc_func_t func, void * param, const arf_interval_t block, slong prec)
 {
@@ -43,7 +31,7 @@ int arb_calc_partition(arf_interval_t L, arf_interval_t R,
     /* Evaluate and get sign at midpoint */
     arb_set_arf(m, u);
     func(t, m, param, 1, prec);
-    msign = _arb_sign(t);
+    msign = arb_sgn_nonzero(t);
 
     /* L, R = block, split at midpoint */
     arf_set(&L->a, &block->a);
@@ -73,11 +61,11 @@ int arb_calc_refine_root_bisect(arf_interval_t r, arb_calc_func_t func,
 
     arb_set_arf(m, &start->a);
     func(v, m, param, 1, prec);
-    asign = _arb_sign(v);
+    asign = arb_sgn_nonzero(v);
 
     arb_set_arf(m, &start->b);
     func(v, m, param, 1, prec);
-    bsign = _arb_sign(v);
+    bsign = arb_sgn_nonzero(v);
 
     /* must have proper sign changes */
     if (asign == 0 || bsign == 0 || asign == bsign)
diff --git a/doc/source/arb.rst b/doc/source/arb.rst
index df47b065..bdacad23 100644
--- a/doc/source/arb.rst
+++ b/doc/source/arb.rst
@@ -599,7 +599,7 @@ Comparisons
     Returns nonzero iff the given number (or ball) *y* is contained in
     the interval represented by *x*.
 
-    If *x* is contains NaN, this function always returns nonzero (as it
+    If *x* contains NaN, this function always returns nonzero (as it
     could represent anything, and in particular could represent all
     the points included in *y*).
     If *y* contains NaN and *x* does not, it always returns zero.
@@ -666,6 +666,12 @@ Arithmetic
     Sets *y* to the sign function of *x*. The result is `[0 \pm 1]` if
     *x* contains both zero and nonzero numbers.
 
+.. function:: int arb_sgn_nonzero(const arb_t x)
+
+    Returns 1 if *x* is strictly positive, -1 if *x* is strictly negative,
+    and 0 if *x* is zero or a ball containing zero so that its sign
+    is not determined.
+
 .. function:: void arb_min(arb_t z, const arb_t x, const arb_t y, slong prec)
 
 .. function:: void arb_max(arb_t z, const arb_t x, const arb_t y, slong prec)