2 files changed, 5 insertions, 1 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 3f12159d169..d202e1d3f38 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,9 @@
 2012-07-18  Paul Eggert  <eggert@cs.ucla.edu>
 
+        * alloc.c (Fmake_bool_vector): Fix off-by-8 bug
+        when invoking (make-bool-vector N t) and N is a positive
+        multiple of 8 -- the last 8 bits were mistakenly cleared.
+
         Remove some struct layout assumptions in bool vectors.
         * alloc.c (bool_header_size): New constant.
         (header_size, word_size): Move earlier, as they're now used earlier.
diff --git a/src/alloc.c b/src/alloc.c
index 29aabdd4616..a6980e867a7 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -2389,7 +2389,7 @@ LENGTH must be a number.  INIT matters only in whether it is t or nil.  */)
 
       /* Clear any extraneous bits in the last byte.  */
       p->data[length_in_chars - 1]
-        &= (1 << (XINT (length) % BOOL_VECTOR_BITS_PER_CHAR)) - 1;
+        &= (1 << ((XFASTINT (length) - 1) % BOOL_VECTOR_BITS_PER_CHAR + 1)) - 1;
     }
 
   return val;