diff --git a/internal/runtime/executor/xai_executor.go b/internal/runtime/executor/xai_executor.go
index 95f71805f..37e1e2970 100644
--- a/internal/runtime/executor/xai_executor.go
+++ b/internal/runtime/executor/xai_executor.go
@@ -727,6 +727,7 @@ func normalizeXAITool(tool gjson.Result) ([]byte, bool, bool) {
 			return nil, false, false
 		}
 		raw = updatedTool
+		toolType = xaiFunctionToolType
 		changed = true
 	}
 	if toolType == xaiWebSearchToolType && tool.Get("external_web_access").Exists() {
@@ -737,6 +738,14 @@ func normalizeXAITool(tool gjson.Result) ([]byte, bool, bool) {
 		raw = updatedTool
 		changed = true
 	}
+	if toolType == xaiFunctionToolType && !tool.Get("parameters").Exists() {
+		updatedTool, errSet := sjson.SetRawBytes(raw, "parameters", []byte(`{"type":"object","properties":{}}`))
+		if errSet != nil {
+			return nil, false, false
+		}
+		raw = updatedTool
+		changed = true
+	}
 	return raw, changed, true
 }
 
diff --git a/internal/runtime/executor/xai_executor_test.go b/internal/runtime/executor/xai_executor_test.go
index 8cc850709..a75f13474 100644
--- a/internal/runtime/executor/xai_executor_test.go
+++ b/internal/runtime/executor/xai_executor_test.go
@@ -123,6 +123,9 @@ func TestXAIExecutorExecuteShapesResponsesRequest(t *testing.T) {
 		if toolType != "function" && toolType != "web_search" {
 			t.Fatalf("tools.%d.type = %q, want function or web_search; body=%s", i, toolType, string(gotBody))
 		}
+		if toolType == "function" && !tool.Get("parameters").Exists() {
+			t.Fatalf("tools.%d.parameters missing for xAI function tool; body=%s", i, string(gotBody))
+		}
 		if got := tool.Get("name").String(); got == "apply_patch" {
 			t.Fatalf("tools.%d.name = apply_patch, want removed; body=%s", i, string(gotBody))
 		}
@@ -261,6 +264,9 @@ func TestXAIExecutorExecuteStreamFiltersToolSearchTool(t *testing.T) {
 		if toolType != "function" && toolType != "web_search" {
 			t.Fatalf("tools.%d.type = %q, want function or web_search; body=%s", i, toolType, string(gotBody))
 		}
+		if toolType == "function" && !tool.Get("parameters").Exists() {
+			t.Fatalf("tools.%d.parameters missing for xAI function tool; body=%s", i, string(gotBody))
+		}
 		if got := tool.Get("name").String(); got == "apply_patch" {
 			t.Fatalf("tools.%d.name = apply_patch, want removed; body=%s", i, string(gotBody))
 		}