diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index c05bf75c46f..b4f1aaca4d5 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -772,6 +772,12 @@ export namespace ProviderTransform {
           result.items = {}
         }
 
+        // Remove properties/required from non-object types (Gemini rejects these)
+        if (result.type && result.type !== "object") {
+          delete result.properties
+          delete result.required
+        }
+
         return result
       }
 
diff --git a/packages/opencode/test/provider/transform.test.ts b/packages/opencode/test/provider/transform.test.ts
index 8e28f1209e1..0743049fe06 100644
--- a/packages/opencode/test/provider/transform.test.ts
+++ b/packages/opencode/test/provider/transform.test.ts
@@ -293,6 +293,116 @@ describe("ProviderTransform.schema - gemini array items", () => {
   })
 })
 
+describe("ProviderTransform.schema - gemini non-object properties removal", () => {
+  const geminiModel = {
+    providerID: "google",
+    api: {
+      id: "gemini-3-pro",
+    },
+  } as any
+
+  test("removes properties from non-object types", () => {
+    const schema = {
+      type: "object",
+      properties: {
+        data: {
+          type: "string",
+          properties: { invalid: { type: "string" } },
+        },
+      },
+    } as any
+
+    const result = ProviderTransform.schema(geminiModel, schema) as any
+
+    expect(result.properties.data.type).toBe("string")
+    expect(result.properties.data.properties).toBeUndefined()
+  })
+
+  test("removes required from non-object types", () => {
+    const schema = {
+      type: "object",
+      properties: {
+        data: {
+          type: "array",
+          items: { type: "string" },
+          required: ["invalid"],
+        },
+      },
+    } as any
+
+    const result = ProviderTransform.schema(geminiModel, schema) as any
+
+    expect(result.properties.data.type).toBe("array")
+    expect(result.properties.data.required).toBeUndefined()
+  })
+
+  test("removes properties and required from nested non-object types", () => {
+    const schema = {
+      type: "object",
+      properties: {
+        outer: {
+          type: "object",
+          properties: {
+            inner: {
+              type: "number",
+              properties: { bad: { type: "string" } },
+              required: ["bad"],
+            },
+          },
+        },
+      },
+    } as any
+
+    const result = ProviderTransform.schema(geminiModel, schema) as any
+
+    expect(result.properties.outer.properties.inner.type).toBe("number")
+    expect(result.properties.outer.properties.inner.properties).toBeUndefined()
+    expect(result.properties.outer.properties.inner.required).toBeUndefined()
+  })
+
+  test("keeps properties and required on object types", () => {
+    const schema = {
+      type: "object",
+      properties: {
+        data: {
+          type: "object",
+          properties: { name: { type: "string" } },
+          required: ["name"],
+        },
+      },
+    } as any
+
+    const result = ProviderTransform.schema(geminiModel, schema) as any
+
+    expect(result.properties.data.type).toBe("object")
+    expect(result.properties.data.properties).toBeDefined()
+    expect(result.properties.data.required).toEqual(["name"])
+  })
+
+  test("does not affect non-gemini providers", () => {
+    const openaiModel = {
+      providerID: "openai",
+      api: {
+        id: "gpt-4",
+      },
+    } as any
+
+    const schema = {
+      type: "object",
+      properties: {
+        data: {
+          type: "string",
+          properties: { invalid: { type: "string" } },
+        },
+      },
+    } as any
+
+    const result = ProviderTransform.schema(openaiModel, schema) as any
+
+    expect(result.properties.data.properties).toBeDefined()
+  })
+})
+
 describe("ProviderTransform.message - DeepSeek reasoning content", () => {
   test("DeepSeek with tool calls includes reasoning_content in providerOptions", () => {
     const msgs = [