diff --git a/builtin-add.c b/builtin-add.c
index cb6e5906fb..2705f8d057 100644
--- a/builtin-add.c
+++ b/builtin-add.c
@@ -11,6 +11,7 @@
 #include "run-command.h"
 #include "parse-options.h"
 #include "diff.h"
+#include "diffcore.h"
 #include "revision.h"
 
 static const char * const builtin_add_usage[] = {
@@ -20,6 +21,81 @@ static const char * const builtin_add_usage[] = {
 static int patch_interactive, add_interactive, edit_interactive;
 static int take_worktree_changes;
 
+struct update_callback_data
+{
+	int flags;
+	int add_errors;
+};
+
+static void update_callback(struct diff_queue_struct *q,
+			    struct diff_options *opt, void *cbdata)
+{
+	int i;
+	struct update_callback_data *data = cbdata;
+
+	for (i = 0; i < q->nr; i++) {
+		struct diff_filepair *p = q->queue[i];
+		const char *path = p->one->path;
+		switch (p->status) {
+		default:
+			die("unexpected diff status %c", p->status);
+		case DIFF_STATUS_UNMERGED:
+			/*
+			 * ADD_CACHE_IGNORE_REMOVAL is unset if "git
+			 * add -u" is calling us, In such a case, a
+			 * missing work tree file needs to be removed
+			 * if there is an unmerged entry at stage #2,
+			 * but such a diff record is followed by
+			 * another with DIFF_STATUS_DELETED (and if
+			 * there is no stage #2, we won't see DELETED
+			 * nor MODIFIED).  We can simply continue
+			 * either way.
+			 */
+			if (!(data->flags & ADD_CACHE_IGNORE_REMOVAL))
+				continue;
+			/*
+			 * Otherwise, it is "git add path" is asking
+			 * to explicitly add it; we fall through.  A
+			 * missing work tree file is an error and is
+			 * caught by add_file_to_index() in such a
+			 * case.
+			 */
+		case DIFF_STATUS_MODIFIED:
+		case DIFF_STATUS_TYPE_CHANGED:
+			if (add_file_to_index(&the_index, path, data->flags)) {
+				if (!(data->flags & ADD_CACHE_IGNORE_ERRORS))
+					die("updating files failed");
+				data->add_errors++;
+			}
+			break;
+		case DIFF_STATUS_DELETED:
+			if (data->flags & ADD_CACHE_IGNORE_REMOVAL)
+				break;
+			if (!(data->flags & ADD_CACHE_PRETEND))
+				remove_file_from_index(&the_index, path);
+			if (data->flags & (ADD_CACHE_PRETEND|ADD_CACHE_VERBOSE))
+				printf("remove '%s'\n", path);
+			break;
+		}
+	}
+}
+
+int add_files_to_cache(const char *prefix, const char **pathspec, int flags)
+{
+	struct update_callback_data data;
+	struct rev_info rev;
+	init_revisions(&rev, prefix);
+	setup_revisions(0, NULL, &rev, NULL);
+	rev.prune_data = pathspec;
+	rev.diffopt.output_format = DIFF_FORMAT_CALLBACK;
+	rev.diffopt.format_callback = update_callback;
+	data.flags = flags;
+	data.add_errors = 0;
+	rev.diffopt.format_callback_data = &data;
+	run_diff_files(&rev, DIFF_RACY_IS_MODIFIED);
+	return !!data.add_errors;
+}
+
 static void fill_pathspec_matches(const char **pathspec, char *seen, int specs)
 {
 	int num_unmatched = 0, i;
diff --git a/read-cache.c b/read-cache.c
index edd995943d..79938bf09a 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -10,9 +10,6 @@
 #include "dir.h"
 #include "tree.h"
 #include "commit.h"
-#include "diff.h"
-#include "diffcore.h"
-#include "revision.h"
 #include "blob.h"
 #include "resolve-undo.h"
 
@@ -1648,81 +1645,6 @@ int read_index_unmerged(struct index_state *istate)
 	return unmerged;
 }
 
-struct update_callback_data
-{
-	int flags;
-	int add_errors;
-};
-
-static void update_callback(struct diff_queue_struct *q,
-			    struct diff_options *opt, void *cbdata)
-{
-	int i;
-	struct update_callback_data *data = cbdata;
-
-	for (i = 0; i < q->nr; i++) {
-		struct diff_filepair *p = q->queue[i];
-		const char *path = p->one->path;
-		switch (p->status) {
-		default:
-			die("unexpected diff status %c", p->status);
-		case DIFF_STATUS_UNMERGED:
-			/*
-			 * ADD_CACHE_IGNORE_REMOVAL is unset if "git
-			 * add -u" is calling us, In such a case, a
-			 * missing work tree file needs to be removed
-			 * if there is an unmerged entry at stage #2,
-			 * but such a diff record is followed by
-			 * another with DIFF_STATUS_DELETED (and if
-			 * there is no stage #2, we won't see DELETED
-			 * nor MODIFIED).  We can simply continue
-			 * either way.
-			 */
-			if (!(data->flags & ADD_CACHE_IGNORE_REMOVAL))
-				continue;
-			/*
-			 * Otherwise, it is "git add path" is asking
-			 * to explicitly add it; we fall through.  A
-			 * missing work tree file is an error and is
-			 * caught by add_file_to_index() in such a
-			 * case.
-			 */
-		case DIFF_STATUS_MODIFIED:
-		case DIFF_STATUS_TYPE_CHANGED:
-			if (add_file_to_index(&the_index, path, data->flags)) {
-				if (!(data->flags & ADD_CACHE_IGNORE_ERRORS))
-					die("updating files failed");
-				data->add_errors++;
-			}
-			break;
-		case DIFF_STATUS_DELETED:
-			if (data->flags & ADD_CACHE_IGNORE_REMOVAL)
-				break;
-			if (!(data->flags & ADD_CACHE_PRETEND))
-				remove_file_from_index(&the_index, path);
-			if (data->flags & (ADD_CACHE_PRETEND|ADD_CACHE_VERBOSE))
-				printf("remove '%s'\n", path);
-			break;
-		}
-	}
-}
-
-int add_files_to_cache(const char *prefix, const char **pathspec, int flags)
-{
-	struct update_callback_data data;
-	struct rev_info rev;
-	init_revisions(&rev, prefix);
-	setup_revisions(0, NULL, &rev, NULL);
-	rev.prune_data = pathspec;
-	rev.diffopt.output_format = DIFF_FORMAT_CALLBACK;
-	rev.diffopt.format_callback = update_callback;
-	data.flags = flags;
-	data.add_errors = 0;
-	rev.diffopt.format_callback_data = &data;
-	run_diff_files(&rev, DIFF_RACY_IS_MODIFIED);
-	return !!data.add_errors;
-}
-
 /*
  * Returns 1 if the path is an "other" path with respect to
  * the index; that is, the path is not mentioned in the index at all,