1 files changed, 1 insertions, 1 deletions

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;