diff --git a/packages/ai/src/utils/schema/normalize.ts b/packages/ai/src/utils/schema/normalize.ts
index 0b1bbd756..d17e439bf 100644
--- a/packages/ai/src/utils/schema/normalize.ts
+++ b/packages/ai/src/utils/schema/normalize.ts
@@ -1086,6 +1086,7 @@ export function sanitizeSchemaForOllama(schema: JsonObject): JsonObject {
 
 		let changed = false;
 		const output: JsonObject = {};
+		let typeAlternatives: JsonObject[] | undefined;
 		for (const key in value) {
 			if (!Object.hasOwn(value, key)) continue;
 			const child = value[key];
@@ -1095,8 +1096,13 @@ export function sanitizeSchemaForOllama(schema: JsonObject): JsonObject {
 			}
 			if (key === "type" && Array.isArray(child)) {
 				const variants = child.filter((entry): entry is string => typeof entry === "string");
-				const nonNull = variants.filter(entry => entry !== "null");
-				output.type = nonNull[0] ?? variants[0] ?? child[0];
+				const uniqueVariants = [...new Set(variants)];
+				const nonNull = uniqueVariants.filter(entry => entry !== "null");
+				if (nonNull.length <= 1) {
+					output.type = nonNull[0] ?? uniqueVariants[0] ?? child[0];
+				} else {
+					typeAlternatives = uniqueVariants.map(entry => ({ type: entry }));
+				}
 				changed = true;
 				continue;
 			}
@@ -1128,6 +1134,11 @@ export function sanitizeSchemaForOllama(schema: JsonObject): JsonObject {
 			output[key] = next;
 		}
 
+		if (typeAlternatives) {
+			const existingAnyOf = output.anyOf;
+			output.anyOf = Array.isArray(existingAnyOf) ? [...typeAlternatives, ...existingAnyOf] : typeAlternatives;
+		}
+
 		return changed ? output : value;
 	};
 	return normalizeNode(schema) as JsonObject;
diff --git a/packages/ai/test/ollama-thinking-disable.test.ts b/packages/ai/test/ollama-thinking-disable.test.ts
index 6116414b5..080044462 100644
--- a/packages/ai/test/ollama-thinking-disable.test.ts
+++ b/packages/ai/test/ollama-thinking-disable.test.ts
@@ -101,6 +101,8 @@ describe("Ollama chat thinking controls", () => {
 				properties: {
 					anything: {},
 					nullableName: { type: ["string", "null"] },
+					stringOrNumber: { type: ["string", "number"] },
+					objectOrArray: { type: ["object", "array"] },
 					list: { type: "array", items: {} },
 					union: { anyOf: [{}, { type: "string" }] },
 					nested: {
@@ -109,7 +111,7 @@ describe("Ollama chat thinking controls", () => {
 						additionalProperties: false,
 					},
 				},
-				required: ["anything", "nullableName", "list", "union", "nested"],
+				required: ["anything", "nullableName", "stringOrNumber", "objectOrArray", "list", "union", "nested"],
 				additionalProperties: false,
 			},
 		};
@@ -143,6 +145,10 @@ describe("Ollama chat thinking controls", () => {
 		expect(Object.hasOwn(parameters, "additionalProperties")).toBe(false);
 		expect(properties.anything).toEqual(widenedOpen);
 		expect(properties.nullableName?.type).toBe("string");
+		expect(properties.stringOrNumber?.anyOf).toEqual([{ type: "string" }, { type: "number" }]);
+		expect(Object.hasOwn(properties.stringOrNumber, "type")).toBe(false);
+		expect(properties.objectOrArray?.anyOf).toEqual([{ type: "object" }, { type: "array" }]);
+		expect(Object.hasOwn(properties.objectOrArray, "type")).toBe(false);
 		expect(properties.list?.items).toEqual(widenedOpen);
 		expect(properties.union?.anyOf).toEqual([widenedOpen, { type: "string" }]);
 		expect(Object.hasOwn(properties.nested, "additionalProperties")).toBe(false);