diff --git a/lang/check/bounds.go b/lang/check/bounds.go
index a2d36ef..6e3c7d9 100644
--- a/lang/check/bounds.go
+++ b/lang/check/bounds.go
@@ -1113,10 +1113,10 @@
 }
 
 func (q *checker) canCopyNFromHistoryFast(recv *a.Expr, args []*a.Node) error {
-	// As per cgen's base-private.h, there are three pre-conditions:
+	// As per cgen's io-private.h, there are three pre-conditions:
 	//  - n <= this.available()
 	//  - distance > 0
-	//  - distance <= this.since_mark().length()
+	//  - distance <= this.history_available()
 
 	if len(args) != 2 {
 		return fmt.Errorf("check: internal error: inconsistent copy_n_from_history_fast arguments")
@@ -1174,7 +1174,7 @@
 		return fmt.Errorf("check: could not prove distance > 0")
 	}
 
-	// Check "distance <= this.since_mark().length()".
+	// Check "distance <= this.history_available()".
 check2:
 	for {
 		for _, x := range q.facts {
@@ -1192,22 +1192,18 @@
 				continue
 			}
 
-			// Check that the RHS is "recv.since_mark().length()".
+			// Check that the RHS is "recv.history_available()".
 			y, method, yArgs := splitReceiverMethodArgs(x.RHS().AsExpr())
-			if method != t.IDLength || len(yArgs) != 0 {
+			if method != t.IDHistoryAvailable || len(yArgs) != 0 {
 				continue
 			}
-			z, method, zArgs := splitReceiverMethodArgs(y)
-			if method != t.IDSinceMark || len(zArgs) != 0 {
-				continue
-			}
-			if !z.Eq(recv) {
+			if !y.Eq(recv) {
 				continue
 			}
 
 			break check2
 		}
-		return fmt.Errorf("check: could not prove distance <= %s.since_mark().length()", recv.Str(q.tm))
+		return fmt.Errorf("check: could not prove distance <= %s.history_available()", recv.Str(q.tm))
 	}
 
 	return nil
diff --git a/release/c/wuffs-unsupported-snapshot.c b/release/c/wuffs-unsupported-snapshot.c
index e0a0e06..41ab2b0 100644
--- a/release/c/wuffs-unsupported-snapshot.c
+++ b/release/c/wuffs-unsupported-snapshot.c
@@ -7709,11 +7709,11 @@
     v_n_copied = 0;
     while (true) {
       if (((uint64_t)((v_dist_minus_1 + 1))) >
-          ((uint64_t)(iop_a_dst - a_dst.private_impl.mark))) {
+          ((uint64_t)(iop_a_dst - a_dst.private_impl.buf->data.ptr))) {
         v_hlen = 0;
-        v_hdist =
-            ((uint32_t)((((uint64_t)((v_dist_minus_1 + 1))) -
-                         ((uint64_t)(iop_a_dst - a_dst.private_impl.mark)))));
+        v_hdist = ((uint32_t)(
+            (((uint64_t)((v_dist_minus_1 + 1))) -
+             ((uint64_t)(iop_a_dst - a_dst.private_impl.buf->data.ptr)))));
         if (v_length > v_hdist) {
           v_length -= v_hdist;
           v_hlen = v_hdist;
@@ -7747,7 +7747,7 @@
           goto label_0_continue;
         }
         if (((uint64_t)((v_dist_minus_1 + 1))) >
-            ((uint64_t)(iop_a_dst - a_dst.private_impl.mark))) {
+            ((uint64_t)(iop_a_dst - a_dst.private_impl.buf->data.ptr))) {
           status = wuffs_deflate__error__internal_error_inconsistent_distance;
           goto exit;
         }
diff --git a/std/deflate/decode_huffman_fast.wuffs b/std/deflate/decode_huffman_fast.wuffs
index d98af1c..6fa3c5f 100644
--- a/std/deflate/decode_huffman_fast.wuffs
+++ b/std/deflate/decode_huffman_fast.wuffs
@@ -292,12 +292,12 @@
 			pre args.dst.available() >= 258,
 		{
 			// Copy from this.history.
-			if ((dist_minus_1 + 1) as base.u64) > args.dst.since_mark().length() {
+			if ((dist_minus_1 + 1) as base.u64) > args.dst.history_available() {
 				// Set (hlen, hdist) to be the length-distance pair to copy
 				// from this.history, and (length, distance) to be the
 				// remaining length-distance pair to copy from args.dst.
 				hlen = 0
-				hdist = (((dist_minus_1 + 1) as base.u64) - args.dst.since_mark().length()) as base.u32
+				hdist = (((dist_minus_1 + 1) as base.u64) - args.dst.history_available()) as base.u32
 				if length > hdist {
 					assert hdist < length via "a < b: b > a"()
 					assert hdist < 0x8000 via "a < b: a < c; c <= b"(c:length)
@@ -345,12 +345,12 @@
 					continue:loop
 				}
 
-				if ((dist_minus_1 + 1) as base.u64) > args.dst.since_mark().length() {
+				if ((dist_minus_1 + 1) as base.u64) > args.dst.history_available() {
 					return "#internal error: inconsistent distance"
 				}
 			}
 			// Once again, redundant but explicit assertions.
-			assert ((dist_minus_1 + 1) as base.u64) <= args.dst.since_mark().length()
+			assert ((dist_minus_1 + 1) as base.u64) <= args.dst.history_available()
 			assert args.dst.available() >= 258
 
 			// We can therefore prove: