diff --git a/dialog/base.go b/dialog/base.go
index d1e99c68a2..e57fb2c4e8 100644
--- a/dialog/base.go
+++ b/dialog/base.go
@@ -54,9 +54,34 @@ func (d *dialog) SetOnClosed(closed func()) {
 	}
 }
 
+// dialogTitle is really just a normal title but we use the Refresh() hook to update the background rectangle.
+type dialogTitle struct {
+	widget.Label
+
+	d *dialog
+}
+
+// Refresh applies the current theme to the whole dialog before refreshing the underlying label.
+func (t *dialogTitle) Refresh() {
+	t.d.applyTheme()
+
+	t.BaseWidget.Refresh()
+}
+
+func newDialogTitle(title string, d *dialog) *dialogTitle {
+	l := &dialogTitle{}
+	l.Text = title
+	l.Alignment = fyne.TextAlignLeading
+	l.TextStyle.Bold = true
+
+	l.d = d
+	l.ExtendBaseWidget(l)
+	return l
+}
+
 func (d *dialog) setButtons(buttons fyne.CanvasObject) {
 	d.bg = canvas.NewRectangle(theme.BackgroundColor())
-	d.label = widget.NewLabelWithStyle(d.title, fyne.TextAlignLeading, fyne.TextStyle{Bold: true})
+	d.label = newDialogTitle(d.title, d)
 
 	var content fyne.CanvasObject
 	if d.icon == nil {
diff --git a/dialog/base_test.go b/dialog/base_test.go
new file mode 100644
index 0000000000..e045f60403
--- /dev/null
+++ b/dialog/base_test.go
@@ -0,0 +1,26 @@
+package dialog
+
+import (
+	"image/color"
+	"testing"
+
+	"fyne.io/fyne"
+	"fyne.io/fyne/canvas"
+	"fyne.io/fyne/test"
+	"fyne.io/fyne/theme"
+	"fyne.io/fyne/widget"
+)
+
+func TestShowCustom_ApplyTheme(t *testing.T) {
+	a := test.NewApp()
+	a.Settings().SetTheme(theme.DarkTheme())
+	w := test.NewWindow(canvas.NewRectangle(color.Transparent))
+	w.Resize(fyne.NewSize(300, 200))
+	d := NewCustom("Title", "OK", widget.NewLabel("Content"), w)
+
+	d.Show()
+	test.AssertImageMatches(t, "dialog-custom-dark.png", w.Canvas().Capture())
+
+	a.Settings().SetTheme(theme.LightTheme())
+	test.AssertImageMatches(t, "dialog-custom-light.png", w.Canvas().Capture())
+}
diff --git a/dialog/file_test.go b/dialog/file_test.go
index 1037509d24..889fb0c6cd 100644
--- a/dialog/file_test.go
+++ b/dialog/file_test.go
@@ -203,7 +203,7 @@ func TestFileFilters(t *testing.T) {
 			count++
 		}
 	}
-	assert.Equal(t, count, 1)
+	assert.Equal(t, 3, count)
 
 	f.SetFilter(storage.NewMimeTypeFileFilter([]string{"image/jpeg"}))
 
@@ -215,7 +215,7 @@ func TestFileFilters(t *testing.T) {
 			count++
 		}
 	}
-	assert.Equal(t, count, 1)
+	assert.Equal(t, 1, count)
 
 	f.SetFilter(storage.NewMimeTypeFileFilter([]string{"image/*"}))
 
@@ -228,5 +228,5 @@ func TestFileFilters(t *testing.T) {
 			count++
 		}
 	}
-	assert.Equal(t, count, 2)
+	assert.Equal(t, 4, count)
 }
diff --git a/dialog/testdata/dialog-custom-dark.png b/dialog/testdata/dialog-custom-dark.png
new file mode 100644
index 0000000000..857712146c
Binary files /dev/null and b/dialog/testdata/dialog-custom-dark.png differ
diff --git a/dialog/testdata/dialog-custom-light.png b/dialog/testdata/dialog-custom-light.png
new file mode 100644
index 0000000000..200abe1ced
Binary files /dev/null and b/dialog/testdata/dialog-custom-light.png differ