diff --git a/midx-write.c b/midx-write.c
index aa438775eb..c50fdb5c6d 100644
--- a/midx-write.c
+++ b/midx-write.c
@@ -133,8 +133,17 @@ static uint32_t midx_pack_perm(struct write_midx_context *ctx,
 static int should_include_pack(const struct write_midx_context *ctx,
 			       const char *file_name)
 {
+	struct multi_pack_index *m = ctx->m;
 	/*
-	 * Note that at most one of ctx->m and ctx->to_include are set,
+	 * When writing incrementally, ctx->m may contain layers above
+	 * the selected base MIDX, which must be included in the new
+	 * layer.
+	 */
+	if (ctx->incremental)
+		m = ctx->base_midx;
+
+	/*
+	 * Note that at most one of m and ctx->to_include are set,
 	 * so we are testing midx_contains_pack() and
 	 * string_list_has_string() independently (guarded by the
 	 * appropriate NULL checks).
@@ -148,10 +157,7 @@ static int should_include_pack(const struct write_midx_context *ctx,
 	 * should be performed independently (likely checking
 	 * to_include before the existing MIDX).
 	 */
-	if (ctx->m && midx_contains_pack(ctx->m, file_name))
-		return 0;
-	else if (ctx->base_midx && midx_contains_pack(ctx->base_midx,
-						      file_name))
+	if (m && midx_contains_pack(m, file_name))
 		return 0;
 	else if (ctx->to_include &&
 		 !string_list_has_string(ctx->to_include, file_name))
diff --git a/t/t5334-incremental-multi-pack-index.sh b/t/t5334-incremental-multi-pack-index.sh
index 69e96bf8d9..84ff612097 100755
--- a/t/t5334-incremental-multi-pack-index.sh
+++ b/t/t5334-incremental-multi-pack-index.sh
@@ -119,7 +119,7 @@ test_expect_success 'write MIDX layer with --base without --no-write-chain-file'
 	test_grep "cannot use --base without --no-write-chain-file" err
 '
 
-test_expect_failure 'write MIDX layer with --base=none and --no-write-chain-file' '
+test_expect_success 'write MIDX layer with --base=none and --no-write-chain-file' '
 	test_commit base-none &&
 	git repack -d &&
 
@@ -136,7 +136,7 @@ test_expect_failure 'write MIDX layer with --base=none and --no-write-chain-file
 	cp "$midx_chain.bak" "$midx_chain"
 '
 
-test_expect_failure 'write MIDX layer with --base=<hash> and --no-write-chain-file' '
+test_expect_success 'write MIDX layer with --base=<hash> and --no-write-chain-file' '
 	test_commit base-hash &&
 	git repack -d &&