diff --git a/internal/lsp/source/util.go b/internal/lsp/source/util.go
index 443bda8eec..56974f22d1 100644
--- a/internal/lsp/source/util.go
+++ b/internal/lsp/source/util.go
@@ -178,25 +178,6 @@ func FileKindForLang(langID string) FileKind {
 	}
 }
 
-func DetectLanguage(langID, filename string) FileKind {
-	// use the langID if the client sent it
-	if kind := FileKindForLang(langID); kind != UnknownKind {
-		return kind
-	}
-	// Detect the language based on the file extension.
-	switch ext := filepath.Ext(filename); ext {
-	case ".mod":
-		return Mod
-	case ".sum":
-		return Sum
-	case ".go":
-		return Go
-	default:
-		// (for instance, before go1.15 cgo files had no extension)
-		return Go
-	}
-}
-
 func (k FileKind) String() string {
 	switch k {
 	case Go: