diff --git a/packages/ai/src/providers/anthropic.ts b/packages/ai/src/providers/anthropic.ts
index 6755c4c4..a52f7322 100644
--- a/packages/ai/src/providers/anthropic.ts
+++ b/packages/ai/src/providers/anthropic.ts
@@ -233,7 +233,7 @@ export const streamAnthropic: StreamFunction<"anthropic-messages", AnthropicOpti
 							name: isOAuthToken
 								? fromClaudeCodeName(event.content_block.name, context.tools)
 								: event.content_block.name,
-							arguments: event.content_block.input as Record<string, any>,
+							arguments: (event.content_block.input as Record<string, any>) ?? {},
 							partialJson: "",
 							index: event.index,
 						};
@@ -619,7 +619,7 @@ function convertMessages(
 						type: "tool_use",
 						id: block.id,
 						name: isOAuthToken ? toClaudeCodeName(block.name) : block.name,
-						input: block.arguments,
+						input: block.arguments ?? {},
 					});
 				}
 			}
diff --git a/packages/ai/src/providers/google-shared.ts b/packages/ai/src/providers/google-shared.ts
index a34e2bd4..a12b454c 100644
--- a/packages/ai/src/providers/google-shared.ts
+++ b/packages/ai/src/providers/google-shared.ts
@@ -143,7 +143,7 @@ export function convertMessages<T extends GoogleApiType>(model: Model<T>, contex
 					// We include a note telling the model this is historical context to prevent mimicry.
 					const isGemini3 = model.id.toLowerCase().includes("gemini-3");
 					if (isGemini3 && !thoughtSignature) {
-						const argsStr = JSON.stringify(block.arguments, null, 2);
+						const argsStr = JSON.stringify(block.arguments ?? {}, null, 2);
 						parts.push({
 							text: `[Historical context: a different model called tool "${block.name}" with arguments: ${argsStr}. Do not mimic this format - use proper function calling.]`,
 						});
@@ -151,7 +151,7 @@ export function convertMessages<T extends GoogleApiType>(model: Model<T>, contex
 						const part: Part = {
 							functionCall: {
 								name: block.name,
-								args: block.arguments,
+								args: block.arguments ?? {},
 								...(requiresToolCallId(model.id) ? { id: block.id } : {}),
 							},
 						};