diff --git a/combobox.go b/combobox.go
index 42e10ac..54403b1 100644
--- a/combobox.go
+++ b/combobox.go
@@ -36,25 +36,23 @@ func NewEditableCombobox(items ...string) *Combobox {
 }
 
 // Append adds items to the end of the Combobox's list.
-func (c *Combobox) Append(what ...string) (err error) {
+// Append will panic if something goes wrong on platforms that do not abort themselves.
+func (c *Combobox) Append(what ...string) {
 	c.lock.Lock()
 	defer c.lock.Unlock()
 
 	if c.created {
 		for i, s := range what {
-			err := c.sysData.append(s)
-			if err != nil {
-				return fmt.Errorf("error adding element %d in Combobox.Append() (%q): %v", i, s, err)
-			}
+			c.sysData.append(s)
 		}
-		return nil
+		return
 	}
 	c.initItems = append(c.initItems, what...)
-	return nil
 }
 
 // InsertBefore inserts a new item in the Combobox before the item at the given position. It panics if the given index is out of bounds.
-func (c *Combobox) InsertBefore(what string, before int) (err error) {
+// InsertBefore will also panic if something goes wrong on platforms that do not abort themselves.
+func (c *Combobox) InsertBefore(what string, before int) {
 	c.lock.Lock()
 	defer c.lock.Unlock()
 
@@ -64,7 +62,8 @@ func (c *Combobox) InsertBefore(what string, before int) (err error) {
 		if before < 0 || before >= c.sysData.len() {
 			goto badrange
 		}
-		return c.sysData.insertBefore(what, before)
+		c.sysData.insertBefore(what, before)
+		return
 	}
 	if before < 0 || before >= len(c.initItems) {
 		goto badrange
@@ -73,7 +72,7 @@ func (c *Combobox) InsertBefore(what string, before int) (err error) {
 	m = append(m, c.initItems[:before]...)
 	m = append(m, what)
 	c.initItems = append(m, c.initItems[before:]...)
-	return nil
+	return
 badrange:
 	panic(fmt.Errorf("index %d out of range in Combobox.InsertBefore()", before))
 }
diff --git a/listbox.go b/listbox.go
index 54c698b..b028bdc 100644
--- a/listbox.go
+++ b/listbox.go
@@ -28,25 +28,23 @@ func NewListbox(multiple bool, items ...string) (l *Listbox) {
 }
 
 // Append adds items to the end of the Listbox's list.
-func (l *Listbox) Append(what ...string) (err error) {
+// Append will panic if something goes wrong on platforms that do not abort themselves.
+func (l *Listbox) Append(what ...string) {
 	l.lock.Lock()
 	defer l.lock.Unlock()
 
 	if l.created {
 		for i, s := range what {
-			err := l.sysData.append(s)
-			if err != nil {
-				return fmt.Errorf("error adding element %d in Listbox.Append() (%q): %v", i, s, err)
-			}
+			l.sysData.append(s)
 		}
-		return nil
+		return
 	}
 	l.initItems = append(l.initItems, what...)
-	return nil
 }
 
 // InsertBefore inserts a new item in the Listbox before the item at the given position. It panics if the given index is out of bounds.
-func (l *Listbox) InsertBefore(what string, before int) (err error) {
+// InsertBefore will also panic if something goes wrong on platforms that do not abort themselves.
+func (l *Listbox) InsertBefore(what string, before int) {
 	l.lock.Lock()
 	defer l.lock.Unlock()
 
@@ -56,7 +54,8 @@ func (l *Listbox) InsertBefore(what string, before int) (err error) {
 		if before < 0 || before >= l.sysData.len() {
 			goto badrange
 		}
-		return l.sysData.insertBefore(what, before)
+		l.sysData.insertBefore(what, before)
+		return
 	}
 	if before < 0 || before >= len(l.initItems) {
 		goto badrange
@@ -65,7 +64,7 @@ func (l *Listbox) InsertBefore(what string, before int) (err error) {
 	m = append(m, l.initItems[:before]...)
 	m = append(m, what)
 	l.initItems = append(m, l.initItems[before:]...)
-	return nil
+	return
 badrange:
 	panic(fmt.Errorf("index %d out of range in Listbox.InsertBefore()", before))
 }
diff --git a/sysdata.go b/sysdata.go
index eb62107..8ee6f3e 100644
--- a/sysdata.go
+++ b/sysdata.go
@@ -40,10 +40,10 @@ func (c *cSysData) isChecked() bool {
 func (c *cSysData) text() string {
 	panic(runtime.GOOS + " sysData does not define text()")
 }
-func (c *cSysData) append(string) error {
+func (c *cSysData) append(string) {
 	panic(runtime.GOOS + " sysData does not define append()")
 }
-func (c *cSysData) insertBefore(string, int) error {
+func (c *cSysData) insertBefore(string, int) {
 	panic(runtime.GOOS + " sysData does not define insertBefore()")
 }
 func (c *cSysData) selectedIndex() int {
diff --git a/sysdata_darwin.go b/sysdata_darwin.go
index 6db7ad3..02e3d8e 100644
--- a/sysdata_darwin.go
+++ b/sysdata_darwin.go
@@ -387,7 +387,7 @@ func (s *sysData) text() string {
 	return <-ret
 }
 
-func (s *sysData) append(what string) error {
+func (s *sysData) append(what string) {
 	ret := make(chan struct{})
 	defer close(ret)
 	uitask <- func() {
@@ -395,10 +395,9 @@ func (s *sysData) append(what string) error {
 		ret <- struct{}{}
 	}
 	<-ret
-	return nil
 }
 
-func (s *sysData) insertBefore(what string, before int) error {
+func (s *sysData) insertBefore(what string, before int) {
 	ret := make(chan struct{})
 	defer close(ret)
 	uitask <- func() {
@@ -406,7 +405,6 @@ func (s *sysData) insertBefore(what string, before int) error {
 		ret <- struct{}{}
 	}
 	<-ret
-	return nil
 }
 
 func (s *sysData) selectedIndex() int {
diff --git a/sysdata_unix.go b/sysdata_unix.go
index f55e463..c07545a 100644
--- a/sysdata_unix.go
+++ b/sysdata_unix.go
@@ -216,7 +216,7 @@ func (s *sysData) text() string {
 	return <-ret
 }
 
-func (s *sysData) append(what string) error {
+func (s *sysData) append(what string) {
 	ret := make(chan struct{})
 	defer close(ret)
 	uitask <- func() {
@@ -224,10 +224,9 @@ func (s *sysData) append(what string) error {
 		ret <- struct{}{}
 	}
 	<-ret
-	return nil
 }
 
-func (s *sysData) insertBefore(what string, before int) error {
+func (s *sysData) insertBefore(what string, before int) {
 	ret := make(chan struct{})
 	defer close(ret)
 	uitask <- func() {
@@ -235,7 +234,6 @@ func (s *sysData) insertBefore(what string, before int) error {
 		ret <- struct{}{}
 	}
 	<-ret
-	return nil
 }
 
 func (s *sysData) selectedIndex() int {
diff --git a/sysdata_windows.go b/sysdata_windows.go
index bf72ba5..4b951f2 100644
--- a/sysdata_windows.go
+++ b/sysdata_windows.go
@@ -317,7 +317,7 @@ func (s *sysData) text() (str string) {
 	return syscall.UTF16ToString(tc)
 }
 
-func (s *sysData) append(what string) (err error) {
+func (s *sysData) append(what string) {
 	ret := make(chan uiret)
 	defer close(ret)
 	uitask <- &uimsg{
@@ -332,14 +332,13 @@ func (s *sysData) append(what string) (err error) {
 	}
 	r := <-ret
 	if r.ret == uintptr(classTypes[s.ctype].addSpaceErr) {
-		return fmt.Errorf("out of space adding item to combobox/listbox (last error: %v)", r.err)
+		panic(fmt.Errorf("out of space adding item to combobox/listbox (last error: %v)", r.err))
 	} else if r.ret == uintptr(classTypes[s.ctype].selectedIndexErr) {
-		return fmt.Errorf("failed to add item to combobox/listbox (last error: %v)", r.err)
+		panic(fmt.Errorf("failed to add item to combobox/listbox (last error: %v)", r.err))
 	}
-	return nil
 }
 
-func (s *sysData) insertBefore(what string, index int) (err error) {
+func (s *sysData) insertBefore(what string, index int) {
 	ret := make(chan uiret)
 	defer close(ret)
 	uitask <- &uimsg{
@@ -354,11 +353,10 @@ func (s *sysData) insertBefore(what string, index int) (err error) {
 	}
 	r := <-ret
 	if r.ret == uintptr(classTypes[s.ctype].addSpaceErr) {
-		return fmt.Errorf("out of space adding item to combobox/listbox (last error: %v)", r.err)
+		panic(fmt.Errorf("out of space adding item to combobox/listbox (last error: %v)", r.err))
 	} else if r.ret == uintptr(classTypes[s.ctype].selectedIndexErr) {
-		return fmt.Errorf("failed to add item to combobox/listbox (last error: %v)", r.err)
+		panic(fmt.Errorf("failed to add item to combobox/listbox (last error: %v)", r.err))
 	}
-	return nil
 }
 
 func (s *sysData) selectedIndex() int {