diff --git a/changes/1821.feature.rst b/changes/1821.feature.rst
new file mode 100644
index 0000000000..4d2b7c02ff
--- /dev/null
+++ b/changes/1821.feature.rst
@@ -0,0 +1 @@
+NumberInput now supports changing alignment on GTK.
diff --git a/examples/textinput/textinput/app.py b/examples/textinput/textinput/app.py
index d9cd39af42..5bca5b7ce0 100644
--- a/examples/textinput/textinput/app.py
+++ b/examples/textinput/textinput/app.py
@@ -17,6 +17,7 @@ def do_extract_values(self, widget, **kwargs):
         self.right_aligned_input.enabled = False
         self.password_input.enabled = False
         self.number_input.enabled = False
+        self.right_aligned_number_input.enabled = False
 
         # Update the labels with the extracted values
         self.text_label.text = "Text content: {}; {}".format(
@@ -29,11 +30,14 @@ def do_extract_values(self, widget, **kwargs):
             self.password_input.value,
         )
 
-        number = self.number_input.value
-        if number:
-            self.number_label.text = f"Double the number is: {number * 2}"
-        else:
-            self.number_label.text = "You didn't enter a number"
+        try:
+            number = self.number_input.value + self.right_aligned_number_input.value
+            self.number_label.text = (
+                f"The sum of {self.number_input.value} and "
+                f"{self.right_aligned_number_input.value} number is: {number}"
+            )
+        except TypeError:
+            self.number_label.text = "Please enter a number in each number input."
 
         # Wait 5 seconds
         for i in range(5, 0, -1):
@@ -47,6 +51,7 @@ def do_extract_values(self, widget, **kwargs):
         self.right_aligned_input.enabled = True
         self.password_input.enabled = True
         self.number_input.enabled = True
+        self.right_aligned_number_input.enabled = True
 
     def startup(self):
         # Set up main window
@@ -75,6 +80,9 @@ def startup(self):
         self.right_aligned_input = toga.TextInput(
             placeholder="Right aligned text", style=Pack(padding=10, text_align=RIGHT)
         )
+        self.right_aligned_number_input = toga.NumberInput(
+            style=Pack(padding=10, text_align=RIGHT)
+        )
         self.password_input = toga.PasswordInput(
             placeholder="Password...",
             style=Pack(padding=10),
@@ -110,6 +118,7 @@ def startup(self):
                 self.password_content_label,
                 self.email_input,
                 self.number_input,
+                self.right_aligned_number_input,
                 self.text_label,
                 self.password_label,
                 self.number_label,
diff --git a/gtk/src/toga_gtk/widgets/numberinput.py b/gtk/src/toga_gtk/widgets/numberinput.py
index 9b09ce232a..1e1bca4566 100644
--- a/gtk/src/toga_gtk/widgets/numberinput.py
+++ b/gtk/src/toga_gtk/widgets/numberinput.py
@@ -3,7 +3,7 @@
 
 from travertino.size import at_least
 
-from ..libs import Gtk
+from ..libs import Gtk, gtk_alignment
 from .base import Widget
 
 
@@ -53,7 +53,8 @@ def set_value(self, value):
             self.native.set_value(self.interface.value)
 
     def set_alignment(self, value):
-        self.interface.factory.not_implemented("NumberInput.set_alignment()")
+        xalign, justify = gtk_alignment(value)
+        self.native.set_alignment(xalign)
 
     def set_font(self, font):
         self.interface.factory.not_implemented("NumberInput.set_font()")