diff --git a/internal/lsp/configuration.go b/internal/lsp/configuration.go
index 31e6e14a..abaee5e0 100644
--- a/internal/lsp/configuration.go
+++ b/internal/lsp/configuration.go
@@ -44,7 +44,7 @@ func (s *Server) didChangeConfiguration(ctx context.Context, _ *protocol.DidChan
 				Method: "textDocument/formatting",
 				RegisterOptions: protocol.TextDocumentRegistrationOptions{
 					DocumentSelector: protocol.DocumentSelector{
-						protocol.DocumentFilter{Language: "ttcn3", Scheme: "file", Pattern: "**/*.ttcn3"},
+						protocol.DocumentFilter{Language: "ttcn3", Scheme: "file", Pattern: "**/*.{ttcn,ttcn3}"},
 					},
 				}})
 		} else {
diff --git a/internal/lsp/general.go b/internal/lsp/general.go
index e3ec612b..3db9facc 100644
--- a/internal/lsp/general.go
+++ b/internal/lsp/general.go
@@ -51,7 +51,7 @@ func newInlayHintRegistrationOptions() *protocol.InlayHintRegistrationOptions {
 		},
 		TextDocumentRegistrationOptions: protocol.TextDocumentRegistrationOptions{
 			DocumentSelector: protocol.DocumentSelector{
-				protocol.DocumentFilter{Language: "ttcn3", Scheme: "file", Pattern: "**/*.ttcn3"},
+				protocol.DocumentFilter{Language: "ttcn3", Scheme: "file", Pattern: "**/*.{ttcn,ttcn3}"},
 			},
 		},
 		StaticRegistrationOptions: protocol.StaticRegistrationOptions{
@@ -65,7 +65,7 @@ func newSemanticTokens() *protocol.SemanticTokensRegistrationOptions {
 
 		TextDocumentRegistrationOptions: protocol.TextDocumentRegistrationOptions{
 			DocumentSelector: protocol.DocumentSelector{
-				protocol.DocumentFilter{Language: "ttcn3", Scheme: "file", Pattern: "**/*.ttcn3"},
+				protocol.DocumentFilter{Language: "ttcn3", Scheme: "file", Pattern: "**/*.{ttcn,ttcn3}"},
 			},
 		},
 		SemanticTokensOptions: protocol.SemanticTokensOptions{