diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index f5ab2f3275f..95e3dc5047c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2016-11-15  Richard Sandiford  <richard.sandiford@arm.com>
+	    Alan Hayward  <alan.hayward@arm.com>
+	    David Sherwood  <david.sherwood@arm.com>
+
+	* rtlanal.c (num_sign_bit_copies1): Calculate bitwidth after
+	handling VOIDmode.
+
 2016-11-15  Matthias Klose  <doko@ubuntu.com>
 
 	* doc/install.texi: Remove references to gcj/libjava.
diff --git a/gcc/rtlanal.c b/gcc/rtlanal.c
index 4617e8ee449..e08f2be789b 100644
--- a/gcc/rtlanal.c
+++ b/gcc/rtlanal.c
@@ -4795,7 +4795,6 @@ num_sign_bit_copies1 (const_rtx x, machine_mode mode, const_rtx known_x,
 		      unsigned int known_ret)
 {
   enum rtx_code code = GET_CODE (x);
-  unsigned int bitwidth = GET_MODE_PRECISION (mode);
   machine_mode inner_mode;
   int num0, num1, result;
   unsigned HOST_WIDE_INT nonzero;
@@ -4811,7 +4810,8 @@ num_sign_bit_copies1 (const_rtx x, machine_mode mode, const_rtx known_x,
       || VECTOR_MODE_P (GET_MODE (x)) || VECTOR_MODE_P (mode))
     return 1;
 
-  /* For a smaller object, just ignore the high bits.  */
+  /* For a smaller mode, just ignore the high bits.  */
+  unsigned int bitwidth = GET_MODE_PRECISION (mode);
   if (bitwidth < GET_MODE_PRECISION (GET_MODE (x)))
     {
       num0 = cached_num_sign_bit_copies (x, GET_MODE (x),