diff --git a/service/dap/server.go b/service/dap/server.go
index cfb67abc33bc6a755c6d0de99aad720ce9c94ee6..1f0eade0c2c718608b296314b64f29f207232838 100644
--- a/service/dap/server.go
+++ b/service/dap/server.go
@@ -432,8 +432,19 @@ func (s *Server) onInitializeRequest(request *dap.InitializeRequest) {
 const debugBinary string = "./__debug_bin"
 
 func (s *Server) onLaunchRequest(request *dap.LaunchRequest) {
-	// TODO(polina): Respond with an error if debug session is in progress?
+	// Validate launch request mode
+	mode, ok := request.Arguments["mode"]
+	if !ok || mode == "" {
+		mode = "debug"
+	}
+	if !isValidLaunchMode(mode) {
+		s.sendErrorResponse(request.Request,
+			FailedToLaunch, "Failed to launch",
+			fmt.Sprintf("Unsupported 'mode' value %q in debug configuration.", mode))
+		return
+	}
 
+	// TODO(polina): Respond with an error if debug session is in progress?
 	program, ok := request.Arguments["program"].(string)
 	if !ok || program == "" {
 		s.sendErrorResponse(request.Request,
@@ -442,11 +453,6 @@ func (s *Server) onLaunchRequest(request *dap.LaunchRequest) {
 		return
 	}
 
-	mode, ok := request.Arguments["mode"]
-	if !ok || mode == "" {
-		mode = "debug"
-	}
-
 	if mode == "debug" || mode == "test" {
 		output, ok := request.Arguments["output"].(string)
 		if !ok || output == "" {
@@ -486,14 +492,6 @@ func (s *Server) onLaunchRequest(request *dap.LaunchRequest) {
 		s.binaryToRemove = debugname
 	}
 
-	// TODO(polina): support "remote" mode
-	if mode != "exec" && mode != "debug" && mode != "test" {
-		s.sendErrorResponse(request.Request,
-			FailedToLaunch, "Failed to launch",
-			fmt.Sprintf("Unsupported 'mode' value %q in debug configuration.", mode))
-		return
-	}
-
 	s.setLaunchAttachArgs(request)
 
 	var targetArgs []string
@@ -535,6 +533,16 @@ func (s *Server) onLaunchRequest(request *dap.LaunchRequest) {
 	s.send(&dap.LaunchResponse{Response: *newResponse(request.Request)})
 }
 
+// TODO(polina): support "remote" mode
+func isValidLaunchMode(launchMode interface{}) bool {
+	switch launchMode {
+	case "exec", "debug", "test":
+		return true
+	}
+
+	return false
+}
+
 // onDisconnectRequest handles the DisconnectRequest. Per the DAP spec,
 // it disconnects the debuggee and signals that the debug adaptor
 // (in our case this TCP server) can be terminated.
diff --git a/service/dap/server_test.go b/service/dap/server_test.go
index 96d6e769352b0fa22b95825ef8950391dd9cac80..02310022dadbc3bafc87d7361b03ba5fd30bff01 100644
--- a/service/dap/server_test.go
+++ b/service/dap/server_test.go
@@ -2559,6 +2559,10 @@ func TestBadLaunchRequests(t *testing.T) {
 		client.LaunchRequestWithArgs(map[string]interface{}{"mode": "debug", "program": fixture.Source, "buildFlags": "123"})
 		expectFailedToLaunch(client.ExpectErrorResponse(t)) // Build error
 
+		client.LaunchRequest("", fixture.Path, stopOnEntry)
+		expectFailedToLaunchWithMessage(client.ExpectErrorResponse(t),
+			"Failed to launch: Build error: exit status 1")
+
 		// We failed to launch the program. Make sure shutdown still works.
 		client.DisconnectRequest()
 		dresp := client.ExpectDisconnectResponse(t)