diff --git a/fmprb.h b/fmprb.h
index 9f7dda72..2c7ae396 100644
--- a/fmprb.h
+++ b/fmprb.h
@@ -164,6 +164,8 @@ void fmprb_log(fmprb_t z, const fmprb_t x, long prec);
 void fmprb_log_ui(fmprb_t z, ulong x, long prec);
 void fmprb_log_fmpz(fmprb_t z, const fmpz_t x, long prec);
 
+void fmprb_fac_ui(fmprb_t x, ulong n, long prec);
+
 void fmprb_const_pi_chudnovsky(fmprb_t x, long prec);
 void fmprb_const_euler_brent_mcmillan(fmprb_t res, long prec);
 void fmprb_const_zeta3_bsplit(fmprb_t x, long prec);
diff --git a/fmprb/fac.c b/fmprb/fac.c
new file mode 100644
index 00000000..d85ca467
--- /dev/null
+++ b/fmprb/fac.c
@@ -0,0 +1,54 @@
+/*=============================================================================
+
+    This file is part of ARB.
+
+    ARB is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    ARB is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with ARB; if not, write to the Free Software
+    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+
+=============================================================================*/
+/******************************************************************************
+
+    Copyright (C) 2012 Fredrik Johansson
+
+******************************************************************************/
+
+#include "fmprb.h"
+
+static void
+fmprb_fac_ui_bsplit(fmprb_t x, ulong a, ulong b, long prec)
+{
+    if (b - a == 1)
+    {
+        fmprb_set_ui(x, b);
+    }
+    else
+    {
+        fmprb_t y;
+        long m = a + (b - a) / 2;
+
+        fmprb_init(y);
+        fmprb_fac_ui_bsplit(x, a, m, prec);
+        fmprb_fac_ui_bsplit(y, m, b, prec);
+        fmprb_mul(x, x, y, prec);
+
+        fmprb_clear(y);
+    }
+}
+
+void
+fmprb_fac_ui(fmprb_t x, ulong n, long prec)
+{
+    fmprb_fac_ui_bsplit(x, ULONG_MAX, FLINT_MAX(n, 1),
+        prec + FLINT_BIT_COUNT(n));
+}