diff --git a/func.go b/func.go
index 16b4305..1cd384b 100644
--- a/func.go
+++ b/func.go
@@ -132,7 +132,7 @@ func (c *Conn) CreateWindowFunction(name string, nArg int, flag FunctionFlag, fn
 			if win, ok := agg.(WindowFunction); ok {
 				return win
 			}
-			return windowFunc{agg, name}
+			return agg
 		}))
 	}
 	rc := res_t(c.call("sqlite3_create_window_function_go",
@@ -307,13 +307,3 @@ func (a *aggregateFunc) Close() error {
 	a.stop()
 	return nil
 }
-
-type windowFunc struct {
-	AggregateFunction
-	name string
-}
-
-func (w windowFunc) Inverse(ctx Context, arg ...Value) {
-	// Implementing inverse allows certain queries that don't really need it to succeed.
-	ctx.ResultError(util.ErrorString(w.name + ": may not be used as a window function"))
-}
diff --git a/internal/util/func.go b/internal/util/func.go
index e705f31..8e89b11 100644
--- a/internal/util/func.go
+++ b/internal/util/func.go
@@ -20,20 +20,6 @@ func ExportFuncVI[T0 i32](mod wazero.HostModuleBuilder, name string, fn func(con
 		Export(name)
 }
 
-type funcVII[T0, T1 i32] func(context.Context, api.Module, T0, T1)
-
-func (fn funcVII[T0, T1]) Call(ctx context.Context, mod api.Module, stack []uint64) {
-	_ = stack[1] // prevent bounds check on every slice access
-	fn(ctx, mod, T0(stack[0]), T1(stack[1]))
-}
-
-func ExportFuncVII[T0, T1 i32](mod wazero.HostModuleBuilder, name string, fn func(context.Context, api.Module, T0, T1)) {
-	mod.NewFunctionBuilder().
-		WithGoModuleFunction(funcVII[T0, T1](fn),
-			[]api.ValueType{api.ValueTypeI32, api.ValueTypeI32}, nil).
-		Export(name)
-}
-
 type funcVIII[T0, T1, T2 i32] func(context.Context, api.Module, T0, T1, T2)
 
 func (fn funcVIII[T0, T1, T2]) Call(ctx context.Context, mod api.Module, stack []uint64) {
diff --git a/tests/conn_test.go b/tests/conn_test.go
index 53a8922..aedcda7 100644
--- a/tests/conn_test.go
+++ b/tests/conn_test.go
@@ -12,7 +12,7 @@ import (
 	"github.com/ncruces/go-sqlite3"
 	_ "github.com/ncruces/go-sqlite3/embed"
 	_ "github.com/ncruces/go-sqlite3/internal/testcfg"
-	_ "github.com/ncruces/go-sqlite3/vfs/memdb"
+	"github.com/ncruces/go-sqlite3/vfs/memdb"
 )
 
 func TestConn_Open_dir(t *testing.T) {
@@ -112,6 +112,48 @@ func TestConn_Close_BUSY(t *testing.T) {
 	}
 }
 
+func TestConn_BusyHandler(t *testing.T) {
+	t.Parallel()
+
+	dsn := memdb.TestDB(t)
+
+	db1, err := sqlite3.Open(dsn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db1.Close()
+
+	db2, err := sqlite3.Open(dsn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db2.Close()
+
+	var called bool
+	err = db2.BusyHandler(func(ctx context.Context, count int) (retry bool) {
+		called = true
+		return count < 1
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tx, err := db1.BeginExclusive()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer tx.End(&err)
+
+	_, err = db2.BeginExclusive()
+	if !errors.Is(err, sqlite3.BUSY) {
+		t.Errorf("got %v, want sqlite3.BUSY", err)
+	}
+
+	if !called {
+		t.Error("busy handler not called")
+	}
+}
+
 func TestConn_SetInterrupt(t *testing.T) {
 	t.Parallel()
 
diff --git a/vfs/memdb/memdb.go b/vfs/memdb/memdb.go
index b990704..5eec5a5 100644
--- a/vfs/memdb/memdb.go
+++ b/vfs/memdb/memdb.go
@@ -76,18 +76,16 @@ func (memVFS) FullPathname(name string) (string, error) {
 type memDB struct {
 	name string
 
+	// +checklocks:lockMtx
+	waiter *sync.Cond
 	// +checklocks:dataMtx
 	data []*[sectorSize]byte
-	// +checklocks:dataMtx
-	size int64
 
-	// +checklocks:memoryMtx
-	refs int32
-
-	shared   int32      // +checklocks:lockMtx
-	pending  bool       // +checklocks:lockMtx
-	reserved bool       // +checklocks:lockMtx
-	waiter   *sync.Cond // +checklocks:lockMtx
+	size     int64 // +checklocks:dataMtx
+	refs     int32 // +checklocks:memoryMtx
+	shared   int32 // +checklocks:lockMtx
+	pending  bool  // +checklocks:lockMtx
+	reserved bool  // +checklocks:lockMtx
 
 	lockMtx sync.Mutex
 	dataMtx sync.RWMutex
@@ -129,7 +127,7 @@ func (m *memFile) ReadAt(b []byte, off int64) (n int, err error) {
 	base := off / sectorSize
 	rest := off % sectorSize
 	have := int64(sectorSize)
-	if base == int64(len(m.data))-1 {
+	if m.size < off+int64(len(b)) {
 		have = modRoundUp(m.size, sectorSize)
 	}
 	n = copy(b, (*m.data[base])[rest:have])
@@ -150,13 +148,13 @@ func (m *memFile) WriteAt(b []byte, off int64) (n int, err error) {
 		m.data = append(m.data, new([sectorSize]byte))
 	}
 	n = copy((*m.data[base])[rest:], b)
+	if size := off + int64(n); size > m.size {
+		m.size = size
+	}
 	if n < len(b) {
 		// notest // assume writes are page aligned
 		return n, io.ErrShortWrite
 	}
-	if size := off + int64(len(b)); size > m.size {
-		m.size = size
-	}
 	return n, nil
 }