diff --git a/func.go b/func.go
index 6b69368..09c1b7a 100644
--- a/func.go
+++ b/func.go
@@ -2,6 +2,7 @@ package sqlite3
 
 import (
 	"context"
+	"io"
 	"sync"
 
 	"github.com/tetratelabs/wazero/api"
@@ -85,12 +86,18 @@ func (c *Conn) CreateWindowFunction(name string, nArg int, flag FunctionFlag, fn
 	var funcPtr ptr_t
 	defer c.arena.mark()()
 	namePtr := c.arena.string(name)
-	if fn != nil {
-		funcPtr = util.AddHandle(c.ctx, fn)
-	}
 	call := "sqlite3_create_aggregate_function_go"
-	if _, ok := fn().(WindowFunction); ok {
-		call = "sqlite3_create_window_function_go"
+	if fn != nil {
+		agg := fn()
+		if c, ok := agg.(io.Closer); ok {
+			if err := c.Close(); err != nil {
+				return err
+			}
+		}
+		if _, ok := agg.(WindowFunction); ok {
+			call = "sqlite3_create_window_function_go"
+		}
+		funcPtr = util.AddHandle(c.ctx, fn)
 	}
 	rc := res_t(c.call(call,
 		stk_t(c.handle), stk_t(namePtr), stk_t(nArg),
@@ -172,7 +179,13 @@ func finalCallback(ctx context.Context, mod api.Module, pCtx, pAgg, pApp ptr_t)
 	db := ctx.Value(connKey{}).(*Conn)
 	fn, handle := callbackAggregate(db, pAgg, pApp)
 	fn.Value(Context{db, pCtx})
-	if err := util.DelHandle(ctx, handle); err != nil {
+	var err error
+	if handle != 0 {
+		err = util.DelHandle(ctx, handle)
+	} else if c, ok := fn.(io.Closer); ok {
+		err = c.Close()
+	}
+	if err != nil {
 		Context{db, pCtx}.ResultError(err)
 		return // notest
 	}