diff --git a/llms/marshaling.go b/llms/marshaling.go
index a9297a97..c0a18a0a 100644
--- a/llms/marshaling.go
+++ b/llms/marshaling.go
@@ -245,10 +245,15 @@ func (tc *ToolCall) UnmarshalJSON(data []byte) error {
 	}
 	var fc FunctionCall
 	fcData, ok := toolCall["function"].(json.RawMessage)
-	if ok {
-		if err := json.Unmarshal(fcData, &fc); err != nil {
-			return fmt.Errorf("error unmarshalling function call: %w", err)
+	if !ok {
+		b, err := json.Marshal(toolCall["function"])
+		if err != nil {
+			return err
 		}
+		fcData = b
+	}
+	if err := json.Unmarshal(fcData, &fc); err != nil {
+		return fmt.Errorf("error unmarshalling function call: %w", err)
 	}
 	tc.ID = id
 	tc.Type = typ
diff --git a/llms/marshaling_test.go b/llms/marshaling_test.go
index 9e3c686b..280fd220 100644
--- a/llms/marshaling_test.go
+++ b/llms/marshaling_test.go
@@ -240,9 +240,12 @@ func TestUnmarshalJSONMessageContent(t *testing.T) {
 				Parts: []ContentPart{
 					TextContent{Text: "Hello there!"},
 					ToolCall{
-						ID:           "t42",
-						Type:         "function",
-						FunctionCall: &FunctionCall{Name: "get_current_weather", Arguments: `{ "location": "New York" }`},
+						ID:   "t42",
+						Type: "function",
+						FunctionCall: &FunctionCall{
+							Name:      "get_current_weather",
+							Arguments: `{ "location": "New York" }`,
+						},
 					},
 				},
 			},
@@ -397,7 +400,14 @@ role: user
 			in: MessageContent{
 				Role: "assistant",
 				Parts: []ContentPart{
-					ToolCall{Type: "function", ID: "t01", FunctionCall: &FunctionCall{Name: "get_current_weather", Arguments: `{ "location": "New York" }`}},
+					ToolCall{
+						Type: "function",
+						ID:   "t01",
+						FunctionCall: &FunctionCall{
+							Name:      "get_current_weather",
+							Arguments: `{ "location": "New York" }`,
+						},
+					},
 				},
 			},
 		},
@@ -406,8 +416,19 @@ role: user
 			in: MessageContent{
 				Role: "assistant",
 				Parts: []ContentPart{
-					ToolCall{Type: "function", ID: "tc01", FunctionCall: &FunctionCall{Name: "get_current_weather", Arguments: `{ "location": "New York" }`}},
-					ToolCall{Type: "function", ID: "tc02", FunctionCall: &FunctionCall{Name: "get_current_weather", Arguments: `{ "location": "Berlin" }`}},
+					ToolCall{
+						Type: "function",
+						ID:   "tc01",
+						FunctionCall: &FunctionCall{
+							Name:      "get_current_weather",
+							Arguments: `{ "location": "New York" }`,
+						},
+					},
+					ToolCall{
+						Type:         "function",
+						ID:           "tc02",
+						FunctionCall: &FunctionCall{Name: "get_current_weather", Arguments: `{ "location": "Berlin" }`},
+					},
 				},
 			},
 			assertedJSON: `{"role":"assistant","parts":[{"type":"tool_call","tool_call":{"function":{"name":"get_current_weather","arguments":"{ \"location\": \"New York\" }"},"id":"tc01","type":"function"}},{"type":"tool_call","tool_call":{"function":{"name":"get_current_weather","arguments":"{ \"location\": \"Berlin\" }"},"id":"tc02","type":"function"}}]}`,
@@ -443,7 +464,10 @@ role: assistant
 			in: MessageContent{
 				Role: "assistant",
 				Parts: []ContentPart{
-					ToolCall{Type: "hammer", FunctionCall: &FunctionCall{Name: "hit", Arguments: `{ "force": 10, "direction": "down" }`}},
+					ToolCall{
+						Type:         "hammer",
+						FunctionCall: &FunctionCall{Name: "hit", Arguments: `{ "force": 10, "direction": "down" }`},
+					},
 				},
 			},
 		},
@@ -533,3 +557,27 @@ role: assistant
 		})
 	}
 }
+
+func TestToolCallSerialization(t *testing.T) {
+	t.Parallel()
+	toolCall := ToolCall{
+		ID:   "test_id",
+		Type: "tool_call",
+		FunctionCall: &FunctionCall{
+			Name:      "getIpLocation",
+			Arguments: `{"ip":"8.8.8.8"}`,
+		},
+	}
+	b, err := json.Marshal(toolCall)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var unmarshalToolCall ToolCall
+	if e := json.Unmarshal(b, &unmarshalToolCall); e != nil {
+		t.Fatal(e)
+	}
+	if diff := cmp.Diff(toolCall, unmarshalToolCall); diff != "" {
+		t.Errorf("")
+	}
+}