diff --git a/setup.c b/setup.c
index f2b070a7a73659..7f23eb4387b79e 100644
--- a/setup.c
+++ b/setup.c
@@ -1221,19 +1221,6 @@ static const char *allowed_bare_repo_to_string(
 	return NULL;
 }
 
-enum discovery_result {
-	GIT_DIR_NONE = 0,
-	GIT_DIR_EXPLICIT,
-	GIT_DIR_DISCOVERED,
-	GIT_DIR_BARE,
-	/* these are errors */
-	GIT_DIR_HIT_CEILING = -1,
-	GIT_DIR_HIT_MOUNT_POINT = -2,
-	GIT_DIR_INVALID_GITFILE = -3,
-	GIT_DIR_INVALID_OWNERSHIP = -4,
-	GIT_DIR_DISALLOWED_BARE = -5,
-};
-
 /*
  * We cannot decide in this function whether we are in the work tree or
  * not, since the config can only be read _after_ this function was called.
@@ -1385,21 +1372,22 @@ static enum discovery_result setup_git_directory_gently_1(struct strbuf *dir,
 	}
 }
 
-int discover_git_directory(struct strbuf *commondir,
-			   struct strbuf *gitdir)
+enum discovery_result discover_git_directory_reason(struct strbuf *commondir,
+						    struct strbuf *gitdir)
 {
 	struct strbuf dir = STRBUF_INIT, err = STRBUF_INIT;
 	size_t gitdir_offset = gitdir->len, cwd_len;
 	size_t commondir_offset = commondir->len;
 	struct repository_format candidate = REPOSITORY_FORMAT_INIT;
+	enum discovery_result result;
 
 	if (strbuf_getcwd(&dir))
-		return -1;
+		return GIT_DIR_CWD_FAILURE;
 
 	cwd_len = dir.len;
-	if (setup_git_directory_gently_1(&dir, gitdir, NULL, 0) <= 0) {
+	if ((result = setup_git_directory_gently_1(&dir, gitdir, NULL, 0)) <= 0) {
 		strbuf_release(&dir);
-		return -1;
+		return result;
 	}
 
 	/*
@@ -1429,11 +1417,11 @@ int discover_git_directory(struct strbuf *commondir,
 		strbuf_setlen(commondir, commondir_offset);
 		strbuf_setlen(gitdir, gitdir_offset);
 		clear_repository_format(&candidate);
-		return -1;
+		return GIT_DIR_INVALID_FORMAT;
 	}
 
 	clear_repository_format(&candidate);
-	return 0;
+	return result;
 }
 
 const char *setup_git_directory_gently(int *nongit_ok)
@@ -1525,9 +1513,11 @@ const char *setup_git_directory_gently(int *nongit_ok)
 		*nongit_ok = 1;
 		break;
 	case GIT_DIR_NONE:
+	case GIT_DIR_CWD_FAILURE:
+	case GIT_DIR_INVALID_FORMAT:
 		/*
 		 * As a safeguard against setup_git_directory_gently_1 returning
-		 * this value, fallthrough to BUG. Otherwise it is possible to
+		 * these values, fallthrough to BUG. Otherwise it is possible to
 		 * set startup_info->have_repository to 1 when we did nothing to
 		 * find a repository.
 		 */
diff --git a/setup.h b/setup.h
index 58fd2605dd2697..b87d0d6fb2b4d1 100644
--- a/setup.h
+++ b/setup.h
@@ -42,6 +42,30 @@ const char *resolve_gitdir_gently(const char *suspect, int *return_error_code);
 #define resolve_gitdir(path) resolve_gitdir_gently((path), NULL)
 
 void setup_work_tree(void);
+
+/*
+ * discover_git_directory_reason() is similar to discover_git_directory(),
+ * except it returns an enum value instead. It is important to note that
+ * a zero-valued return here is actually GIT_DIR_NONE, which is different
+ * from discover_git_directory.
+ */
+enum discovery_result {
+	GIT_DIR_NONE = 0,
+	GIT_DIR_EXPLICIT,
+	GIT_DIR_DISCOVERED,
+	GIT_DIR_BARE,
+	/* these are errors */
+	GIT_DIR_HIT_CEILING = -1,
+	GIT_DIR_HIT_MOUNT_POINT = -2,
+	GIT_DIR_INVALID_GITFILE = -3,
+	GIT_DIR_INVALID_OWNERSHIP = -4,
+	GIT_DIR_DISALLOWED_BARE = -5,
+	GIT_DIR_INVALID_FORMAT = -6,
+	GIT_DIR_CWD_FAILURE = -7,
+};
+enum discovery_result discover_git_directory_reason(struct strbuf *commondir,
+						    struct strbuf *gitdir);
+
 /*
  * Find the commondir and gitdir of the repository that contains the current
  * working directory, without changing the working directory or other global
@@ -50,8 +74,12 @@ void setup_work_tree(void);
  * both have the same result appended to the buffer.  The return value is
  * either 0 upon success and non-zero if no repository was found.
  */
-int discover_git_directory(struct strbuf *commondir,
-			   struct strbuf *gitdir);
+static inline int discover_git_directory(struct strbuf *commondir,
+					 struct strbuf *gitdir)
+{
+	return discover_git_directory_reason(commondir, gitdir) <= 0;
+}
+
 const char *setup_git_directory_gently(int *);
 const char *setup_git_directory(void);
 char *prefix_path(const char *prefix, int len, const char *path);