diff --git a/internal/index/index.go b/internal/index/index.go
index 19f16f8..a93a8ce 100644
--- a/internal/index/index.go
+++ b/internal/index/index.go
@@ -5,7 +5,6 @@ import (
 	"path/filepath"
 	"strings"
 
-	"github.com/marte-community/marte-dev-tools/internal/logger"
 	"github.com/marte-community/marte-dev-tools/internal/parser"
 )
 
@@ -456,9 +455,7 @@ type QueryResult struct {
 }
 
 func (pt *ProjectTree) Query(file string, line, col int) *QueryResult {
-	logger.Printf("File: %s:%d:%d", file, line, col)
 	for i := range pt.References {
-		logger.Printf("%s", pt.Root.Name)
 		ref := &pt.References[i]
 		if ref.File == file {
 			if line == ref.Position.Line && col >= ref.Position.Column && col < ref.Position.Column+len(ref.Name) {
diff --git a/internal/lsp/server.go b/internal/lsp/server.go
index 0f4ee9e..cd7f97c 100644
--- a/internal/lsp/server.go
+++ b/internal/lsp/server.go
@@ -222,6 +222,12 @@ func readMessage(reader *bufio.Reader) (*JsonRpcMessage, error) {
 }
 
 func HandleMessage(msg *JsonRpcMessage) {
+	defer func() {
+		if r := recover(); r != nil {
+			logger.Printf("Panic in HandleMessage: %v", r)
+		}
+	}()
+
 	switch msg.Method {
 	case "initialize":
 		var params InitializeParams
@@ -1326,10 +1332,10 @@ func HandleRename(params RenameParams) *WorkspaceEdit {
 }
 
 func respond(id any, result any) {
-	msg := JsonRpcMessage{
-		Jsonrpc: "2.0",
-		ID:      id,
-		Result:  result,
+	msg := map[string]any{
+		"jsonrpc": "2.0",
+		"id":      id,
+		"result":  result,
 	}
 	send(msg)
 }
diff --git a/test/lsp_completion_signals_robustness_test.go b/test/lsp_completion_signals_robustness_test.go
index f1dd0b5..a5f2283 100644
--- a/test/lsp_completion_signals_robustness_test.go
+++ b/test/lsp_completion_signals_robustness_test.go
@@ -61,7 +61,7 @@ package schema
 	found := false
 	if listIn != nil {
 		for _, item := range listIn.Items {
-			if item.Label == "Sig:DS" {
+			if item.Label == "DS:Sig" {
 				found = true
 			}
 		}
@@ -79,7 +79,7 @@ package schema
 	found = false
 	if listOut != nil {
 		for _, item := range listOut.Items {
-			if item.Label == "Sig:DS" {
+			if item.Label == "DS:Sig" {
 				found = true
 			}
 		}
diff --git a/test/lsp_completion_signals_test.go b/test/lsp_completion_signals_test.go
index 47a4a9d..46fc18a 100644
--- a/test/lsp_completion_signals_test.go
+++ b/test/lsp_completion_signals_test.go
@@ -75,7 +75,7 @@ package schema
 	foundIn := false
 	foundOut := false
 	for _, item := range listIn.Items {
-		if item.Label == "InSig:InDS" {
+		if item.Label == "InDS:InSig" {
 			foundIn = true
 			// Normalize spaces for check
 			insert := strings.ReplaceAll(item.InsertText, " ", "")
@@ -85,16 +85,16 @@ package schema
 				t.Errorf("InsertText mismatch: %s", item.InsertText)
 			}
 		}
-		if item.Label == "OutSig:OutDS" {
+		if item.Label == "OutDS:OutSig" {
 			foundOut = true
 		}
 	}
 
 	if !foundIn {
-		t.Error("Did not find InSig:InDS")
+		t.Error("Did not find InDS:InSig")
 	}
 	if foundOut {
-		t.Error("Should not find OutSig:OutDS in InputSignals")
+		t.Error("Should not find OutDS:OutSig in InputSignals")
 	}
 
 	// 2. Suggest in OutputSignals
@@ -111,18 +111,18 @@ package schema
 	foundIn = false
 	foundOut = false
 	for _, item := range listOut.Items {
-		if item.Label == "InSig:InDS" {
+		if item.Label == "InDS:InSig" {
 			foundIn = true
 		}
-		if item.Label == "OutSig:OutDS" {
+		if item.Label == "OutDS:OutSig" {
 			foundOut = true
 		}
 	}
 
 	if foundIn {
-		t.Error("Should not find InSig:InDS in OutputSignals")
+		t.Error("Should not find InDS:InSig in OutputSignals")
 	}
 	if !foundOut {
-		t.Error("Did not find OutSig:OutDS in OutputSignals")
+		t.Error("Did not find OutDS:OutSig in OutputSignals")
 	}
 }
diff --git a/test/lsp_crash_test.go b/test/lsp_crash_test.go
new file mode 100644
index 0000000..88215b0
--- /dev/null
+++ b/test/lsp_crash_test.go
@@ -0,0 +1,74 @@
+package integration
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/marte-community/marte-dev-tools/internal/index"
+	"github.com/marte-community/marte-dev-tools/internal/lsp"
+	"github.com/marte-community/marte-dev-tools/internal/parser"
+)
+
+func TestLSPCrashOnUndefinedReference(t *testing.T) {
+	// Setup
+	lsp.Tree = index.NewProjectTree()
+	lsp.Documents = make(map[string]string)
+
+	content := `
++App = {
+    Class = RealTimeApplication
+    +State = {
+        Class = RealTimeState
+        +Thread = {
+            Class = RealTimeThread
+            Functions = { UndefinedGAM }
+        }
+    }
+}
+`
+	uri := "file://crash.marte"
+	lsp.Documents[uri] = content
+	p := parser.NewParser(content)
+	cfg, err := p.Parse()
+	if err != nil {
+		t.Fatal(err)
+	}
+	lsp.Tree.AddFile("crash.marte", cfg)
+	lsp.Tree.ResolveReferences()
+
+	// Line 7: "            Functions = { UndefinedGAM }"
+	// 12 spaces + "Functions" (9) + " = { " (5) = 26 chars prefix.
+	// UndefinedGAM starts at 26.
+	params := lsp.DefinitionParams{
+		TextDocument: lsp.TextDocumentIdentifier{URI: uri},
+		Position:     lsp.Position{Line: 7, Character: 27},
+	}
+
+	// This should NOT panic
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("Recovered from panic: %v", r)
+		}
+	}()
+
+	res := lsp.HandleDefinition(params)
+
+	if res != nil {
+		t.Error("Expected nil for undefined reference definition")
+	}
+
+	// 2. Hover
+	hParams := lsp.HoverParams{
+		TextDocument: lsp.TextDocumentIdentifier{URI: uri},
+		Position:     lsp.Position{Line: 7, Character: 27},
+	}
+	hover := lsp.HandleHover(hParams)
+	if hover == nil {
+		t.Error("Expected hover for unresolved reference")
+	} else {
+		content := hover.Contents.(lsp.MarkupContent).Value
+		if !strings.Contains(content, "Unresolved") {
+			t.Errorf("Expected 'Unresolved' in hover, got: %s", content)
+		}
+	}
+}