diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index f19c1fc0bd9e..73edac7b801a 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,7 @@
+2012-10-24  Richard Sandiford  <rdsandiford@googlemail.com>
+
+	* expmed.c (lowpart_bit_field_p): Add missing == 0 check.
+
 2012-10-24  Vladimir Makarov  <vmakarov@redhat.com>
 
 	PR bootstrap/55049
diff --git a/gcc/expmed.c b/gcc/expmed.c
index 1708f57f0be6..6d9b13354cb1 100644
--- a/gcc/expmed.c
+++ b/gcc/expmed.c
@@ -402,7 +402,7 @@ lowpart_bit_field_p (unsigned HOST_WIDE_INT bitnum,
 		     enum machine_mode struct_mode)
 {
   if (BYTES_BIG_ENDIAN)
-    return (bitnum % BITS_PER_UNIT
+    return (bitnum % BITS_PER_UNIT == 0
 	    && (bitnum + bitsize == GET_MODE_BITSIZE (struct_mode)
 		|| (bitnum + bitsize) % BITS_PER_WORD == 0));
   else