diff --git a/internal/provider/gemini.go b/internal/provider/gemini.go
index 54a235f..f20ed6a 100644
--- a/internal/provider/gemini.go
+++ b/internal/provider/gemini.go
@@ -157,10 +157,7 @@ func (c *geminiClient) buildRequest(req Request) (*gemRequest, string, error) {
 	if functionsEnabled && len(req.Tools) > 0 {
 		decls := make([]gemFunctionDecl, 0, len(req.Tools))
 		for _, t := range req.Tools {
-			schema := t.Schema
-			if len(schema) == 0 || !json.Valid(schema) {
-				schema = json.RawMessage(`{"type":"object","properties":{}}`)
-			}
+			schema := sanitizeGeminiToolSchema(t.Schema)
 			decls = append(decls, gemFunctionDecl{
 				Name:        t.Name,
 				Description: t.Description,
@@ -226,6 +223,46 @@ func (c *geminiClient) buildRequest(req Request) (*gemRequest, string, error) {
 	return out, m.ID, nil
 }
 
+func sanitizeGeminiToolSchema(schema json.RawMessage) json.RawMessage {
+	if len(schema) == 0 || !json.Valid(schema) {
+		return json.RawMessage(`{"type":"object","properties":{}}`)
+	}
+	var v any
+	if err := json.Unmarshal(schema, &v); err != nil {
+		return json.RawMessage(`{"type":"object","properties":{}}`)
+	}
+	v = stripGeminiUnsupportedSchemaFields(v)
+	out, err := json.Marshal(v)
+	if err != nil || len(out) == 0 || !json.Valid(out) {
+		return json.RawMessage(`{"type":"object","properties":{}}`)
+	}
+	return out
+}
+
+func stripGeminiUnsupportedSchemaFields(v any) any {
+	switch x := v.(type) {
+	case map[string]any:
+		out := make(map[string]any, len(x))
+		for k, val := range x {
+			switch k {
+			case "additionalProperties", "$schema":
+				continue
+			default:
+				out[k] = stripGeminiUnsupportedSchemaFields(val)
+			}
+		}
+		return out
+	case []any:
+		out := make([]any, len(x))
+		for i, val := range x {
+			out[i] = stripGeminiUnsupportedSchemaFields(val)
+		}
+		return out
+	default:
+		return v
+	}
+}
+
 func convertGemUserParts(blocks []Content) []gemPart {
 	var parts []gemPart
 	for _, b := range blocks {
diff --git a/internal/provider/gemini_test.go b/internal/provider/gemini_test.go
index a46ba2c..a379fee 100644
--- a/internal/provider/gemini_test.go
+++ b/internal/provider/gemini_test.go
@@ -206,6 +206,42 @@ func TestGeminiBuildRequestSystemAndTools(t *testing.T) {
 
 // TestGeminiBuildRequestImageModelOmitsTools confirms image-generation
 // models receive direct multimodal prompts without function declarations.
+func TestGeminiBuildRequestStripsUnsupportedSchemaFields(t *testing.T) {
+	c := NewGemini("k", "https://example.invalid").(*geminiClient)
+	wire, _, err := c.buildRequest(Request{
+		Model: "gemini-2.5-pro",
+		Tools: []Tool{{
+			Name:        "edit",
+			Description: "edit a file",
+			Schema: json.RawMessage(`{
+				"$schema":"http://json-schema.org/draft-07/schema#",
+				"type":"object",
+				"additionalProperties":false,
+				"properties":{
+					"edits":{
+						"type":"array",
+						"items":{
+							"type":"object",
+							"additionalProperties":false,
+							"properties":{"oldText":{"type":"string"},"newText":{"type":"string"}}
+						}
+					}
+				}
+			}`),
+		}},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := string(wire.Tools[0].FunctionDeclarations[0].Parameters)
+	if strings.Contains(got, "additionalProperties") || strings.Contains(got, "$schema") {
+		t.Fatalf("Gemini schema should strip unsupported fields, got %s", got)
+	}
+	if !strings.Contains(got, `"oldText"`) || !strings.Contains(got, `"newText"`) {
+		t.Fatalf("Gemini schema lost nested properties, got %s", got)
+	}
+}
+
 func TestGeminiBuildRequestImageModelOmitsTools(t *testing.T) {
 	c := NewGemini("k", "https://example.invalid").(*geminiClient)
 	wire, _, err := c.buildRequest(Request{