diff --git a/lib/int128/sail.c b/lib/int128/sail.c
index 3d559ba98..81ac783b0 100644
--- a/lib/int128/sail.c
+++ b/lib/int128/sail.c
@@ -909,23 +909,6 @@ void vector_update_subrange_lbits(lbits *rop,
   }
 }
 
-fbits fast_update_subrange(const fbits op,
-			   const mach_int n,
-			   const mach_int m,
-			   const fbits slice)
-{
-  fbits rop = op;
-  for (mach_int i = 0; i < n - (m - UINT64_C(1)); i++) {
-    uint64_t bit = UINT64_C(1) << ((uint64_t) i);
-    if (slice & bit) {
-      rop |= (bit << m);
-    } else {
-      rop &= ~(bit << m);
-    }
-  }
-  return rop;
-}
-
 __attribute__((target ("bmi2")))
 void slice(lbits *rop, const lbits op, const sail_int start_big, const sail_int len_big)
 {
diff --git a/lib/int128/sail.h b/lib/int128/sail.h
index 51a16b93a..b3950f6ff 100644
--- a/lib/int128/sail.h
+++ b/lib/int128/sail.h
@@ -294,11 +294,6 @@ void vector_update_subrange_lbits(lbits *rop,
 				      const sail_int m_mpz,
 				      const lbits slice);
 
-fbits fast_update_subrange(const fbits op,
-			   const mach_int n,
-			   const mach_int m,
-			   const fbits slice);
-
 void slice(lbits *rop, const lbits op, const sail_int start_mpz, const sail_int len_mpz);
 
 sbits sslice(const fbits op, const mach_int start, const mach_int len);
diff --git a/lib/sail.c b/lib/sail.c
index 31605e63d..a73216ce4 100644
--- a/lib/sail.c
+++ b/lib/sail.c
@@ -1154,23 +1154,6 @@ void vector_update_subrange_inc_lbits(lbits *rop,
   }
 }
 
-fbits fast_update_subrange(const fbits op,
-			   const mach_int n,
-			   const mach_int m,
-			   const fbits slice)
-{
-  fbits rop = op;
-  for (mach_int i = 0; i < n - (m - UINT64_C(1)); i++) {
-    uint64_t bit = UINT64_C(1) << ((uint64_t) i);
-    if (slice & bit) {
-      rop |= (bit << m);
-    } else {
-      rop &= ~(bit << m);
-    }
-  }
-  return rop;
-}
-
 void slice(lbits *rop, const lbits op, const sail_int start_mpz, const sail_int len_mpz)
 {
   assert(mpz_get_ui(start_mpz) + mpz_get_ui(len_mpz) <= op.len);
diff --git a/lib/sail.h b/lib/sail.h
index 1fb9c7998..eb6ad617e 100644
--- a/lib/sail.h
+++ b/lib/sail.h
@@ -398,11 +398,6 @@ void vector_update_subrange_inc_lbits(lbits *rop,
 				      const sail_int m_mpz,
 				      const lbits slice);
 
-fbits fast_update_subrange(const fbits op,
-			   const mach_int n,
-			   const mach_int m,
-			   const fbits slice);
-
 void slice(lbits *rop, const lbits op, const sail_int start_mpz, const sail_int len_mpz);
 void slice_inc(lbits *rop, const lbits op, const sail_int start_mpz, const sail_int len_mpz);