diff --git a/kittens/diff/highlight.go b/kittens/diff/highlight.go
index 8bf3755e9f..a83525c664 100644
--- a/kittens/diff/highlight.go
+++ b/kittens/diff/highlight.go
@@ -183,6 +183,7 @@ func resolved_chroma_style() *chroma.Style {
 }
 
 var tokens_map map[string][]chroma.Token
+var mu sync.Mutex
 
 func highlight_file(path string) (highlighted string, err error) {
 	defer func() {
@@ -210,7 +211,9 @@ func highlight_file(path string) (highlighted string, err error) {
 	if tokens_map == nil {
 		tokens_map = make(map[string][]chroma.Token)
 	}
+	mu.Lock()
 	tokens := tokens_map[path]
+	mu.Unlock()
 	if tokens == nil {
 		lexer := lexers.Match(filename_for_detection)
 		if lexer == nil {
@@ -225,7 +228,9 @@ func highlight_file(path string) (highlighted string, err error) {
 			return "", err
 		}
 		tokens = iterator.Tokens()
+		mu.Lock()
 		tokens_map[path] = tokens
+		mu.Unlock()
 	}
 	formatter := chroma.FormatterFunc(ansi_formatter)
 	w := strings.Builder{}