diff --git a/add-patch.c b/add-patch.c
index 9c0f3b23ef..fac82c3886 100644
--- a/add-patch.c
+++ b/add-patch.c
@@ -4,11 +4,13 @@
 #include "git-compat-util.h"
 #include "add-patch.h"
 #include "advice.h"
+#include "commit.h"
 #include "config.h"
 #include "diff.h"
 #include "editor.h"
 #include "environment.h"
 #include "gettext.h"
+#include "hex.h"
 #include "object-name.h"
 #include "pager.h"
 #include "read-cache-ll.h"
@@ -263,6 +265,8 @@ struct hunk {
 
 struct add_p_state {
 	struct repository *r;
+	struct index_state *index;
+	const char *index_file;
 	struct interactive_config cfg;
 	struct strbuf answer, buf;
 
@@ -437,7 +441,7 @@ static void setup_child_process(struct add_p_state *s,
 
 	cp->git_cmd = 1;
 	strvec_pushf(&cp->env,
-		     INDEX_ENVIRONMENT "=%s", s->r->index_file);
+		     INDEX_ENVIRONMENT "=%s", s->index_file);
 }
 
 static int parse_range(const char **p,
@@ -1861,7 +1865,7 @@ soft_increment:
 		strbuf_reset(&s->buf);
 		reassemble_patch(s, file_diff, 0, &s->buf);
 
-		discard_index(s->r->index);
+		discard_index(s->index);
 		if (s->mode->apply_for_checkout)
 			apply_for_checkout(s, &s->buf,
 					   s->mode->is_reverse);
@@ -1872,9 +1876,11 @@ soft_increment:
 					 NULL, 0, NULL, 0))
 				error(_("'git apply' failed"));
 		}
-		if (repo_read_index(s->r) >= 0)
+		if (read_index_from(s->index, s->index_file, s->r->gitdir) >= 0 &&
+		    s->index == s->r->index) {
 			repo_refresh_and_write_index(s->r, REFRESH_QUIET, 0,
 						     1, NULL, NULL, NULL);
+		}
 	}
 
 	putchar('\n');
@@ -1887,6 +1893,8 @@ int run_add_p(struct repository *r, enum add_p_mode mode,
 {
 	struct add_p_state s = {
 		.r = r,
+		.index = r->index,
+		.index_file = r->index_file,
 		.answer = STRBUF_INIT,
 		.buf = STRBUF_INIT,
 		.plain = STRBUF_INIT,
@@ -1945,3 +1953,99 @@ int run_add_p(struct repository *r, enum add_p_mode mode,
 	add_p_state_clear(&s);
 	return 0;
 }
+
+int run_add_p_index(struct repository *r,
+		    struct index_state *index,
+		    const char *index_file,
+		    struct interactive_options *opts,
+		    const char *revision,
+		    const struct pathspec *ps)
+{
+	struct patch_mode mode = {
+		.apply_args = { "--cached", NULL },
+		.apply_check_args = { "--cached", NULL },
+		.prompt_mode = {
+			N_("Stage mode change [y,n,q,a,d%s,?]? "),
+			N_("Stage deletion [y,n,q,a,d%s,?]? "),
+			N_("Stage addition [y,n,q,a,d%s,?]? "),
+			N_("Stage this hunk [y,n,q,a,d%s,?]? ")
+		},
+		.edit_hunk_hint = N_("If the patch applies cleanly, the edited hunk "
+				     "will immediately be marked for staging."),
+		.help_patch_text =
+			N_("y - stage this hunk\n"
+			   "n - do not stage this hunk\n"
+			   "q - quit; do not stage this hunk or any of the remaining "
+				"ones\n"
+			   "a - stage this hunk and all later hunks in the file\n"
+			   "d - do not stage this hunk or any of the later hunks in "
+				"the file\n"),
+		.index_only = 1,
+	};
+	struct add_p_state s = {
+		.r = r,
+		.index = index,
+		.index_file = index_file,
+		.answer = STRBUF_INIT,
+		.buf = STRBUF_INIT,
+		.plain = STRBUF_INIT,
+		.colored = STRBUF_INIT,
+		.mode = &mode,
+		.revision = revision,
+	};
+	struct strbuf parent_revision = STRBUF_INIT;
+	char parent_tree_oid[GIT_MAX_HEXSZ + 1];
+	size_t binary_count = 0;
+	struct commit *commit;
+	int ret;
+
+	commit = lookup_commit_reference_by_name(revision);
+	if (!commit) {
+		err(&s, _("Revision does not refer to a commit"));
+		ret = -1;
+		goto out;
+	}
+
+	if (commit->parents)
+		oid_to_hex_r(parent_tree_oid, get_commit_tree_oid(commit->parents->item));
+	else
+		oid_to_hex_r(parent_tree_oid, r->hash_algo->empty_tree);
+
+	strbuf_addf(&parent_revision, "%s~", revision);
+	mode.diff_cmd[0] = "diff-tree";
+	mode.diff_cmd[1] = "-r";
+	mode.diff_cmd[2] = parent_tree_oid;
+
+	interactive_config_init(&s.cfg, r, opts);
+
+	if (parse_diff(&s, ps) < 0) {
+		ret = -1;
+		goto out;
+	}
+
+	for (size_t i = 0; i < s.file_diff_nr; i++) {
+		if (s.file_diff[i].binary && !s.file_diff[i].hunk_nr)
+			binary_count++;
+		else if (patch_update_file(&s, s.file_diff + i))
+			break;
+	}
+
+	if (s.file_diff_nr == 0) {
+		err(&s, _("No changes."));
+		ret = -1;
+		goto out;
+	}
+
+	if (binary_count == s.file_diff_nr) {
+		err(&s, _("Only binary files changed."));
+		ret = -1;
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	strbuf_release(&parent_revision);
+	add_p_state_clear(&s);
+	return ret;
+}
diff --git a/add-patch.h b/add-patch.h
index a4a05d9d14..901c42fd7b 100644
--- a/add-patch.h
+++ b/add-patch.h
@@ -3,6 +3,7 @@
 
 #include "color.h"
 
+struct index_state;
 struct pathspec;
 struct repository;
 
@@ -53,4 +54,11 @@ int run_add_p(struct repository *r, enum add_p_mode mode,
 	      struct interactive_options *opts, const char *revision,
 	      const struct pathspec *ps);
 
+int run_add_p_index(struct repository *r,
+		    struct index_state *index,
+		    const char *index_file,
+		    struct interactive_options *opts,
+		    const char *revision,
+		    const struct pathspec *ps);
+
 #endif