diff --git a/docs/changelog.rst b/docs/changelog.rst
index 175aa73b5..880bb9bd4 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -42,6 +42,8 @@ Detailed list of changes
 
 - Fix a regression in the previous release that broke handling of some key board shortcuts in some kittens on some keyboard layouts (:iss:`6189`)
 
+- Fix a regression in the previous release that broke usage of custom themes (:iss:`6191`)
+
 0.28.0 [2023-04-15]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/tools/themes/collection.go b/tools/themes/collection.go
index 12874d75a..34499a3c4 100644
--- a/tools/themes/collection.go
+++ b/tools/themes/collection.go
@@ -532,10 +532,11 @@ func parse_theme_metadata(path string) (*ThemeMetadata, map[string]string, error
 type Theme struct {
 	metadata *ThemeMetadata
 
-	code            string
-	settings        map[string]string
-	zip_reader      *zip.File
-	is_user_defined bool
+	code                        string
+	settings                    map[string]string
+	zip_reader                  *zip.File
+	is_user_defined             bool
+	path_for_user_defined_theme string
 }
 
 func (self *Theme) Name() string        { return self.metadata.Name }
@@ -558,6 +559,13 @@ func (self *Theme) load_code() (string, error) {
 		}
 		self.code = utils.UnsafeBytesToString(data)
 	}
+	if self.is_user_defined && self.path_for_user_defined_theme != "" && self.code == "" {
+		raw, err := os.ReadFile(self.path_for_user_defined_theme)
+		if err != nil {
+			return "", err
+		}
+		self.code = utils.UnsafeBytesToString(raw)
+	}
 	return self.code, nil
 }
 
@@ -813,7 +821,7 @@ func (self *Themes) AddFromFile(path string) (*Theme, error) {
 	if m.Name == "" {
 		m.Name = theme_name_from_file_name(filepath.Base(path))
 	}
-	t := Theme{metadata: m, is_user_defined: true, settings: conf}
+	t := Theme{metadata: m, is_user_defined: true, settings: conf, path_for_user_defined_theme: path}
 	self.name_map[m.Name] = &t
 	return &t, nil