diff --git a/subiquity/ui/views/filesystem/partition.py b/subiquity/ui/views/filesystem/partition.py
index 1e7cd7f072..c81abf851f 100644
--- a/subiquity/ui/views/filesystem/partition.py
+++ b/subiquity/ui/views/filesystem/partition.py
@@ -89,6 +89,7 @@ def _make_widget(self, form):
 class SizeWidget(StringEditor):
     def __init__(self, form):
         self.form = form
+        self.accurate_value: Optional[int] = None
         super().__init__()
 
     def lost_focus(self):
@@ -114,6 +115,9 @@ def lost_focus(self):
                     ),
                 )
             )
+            # This will invoke self.form.clean_size() and it is expected that
+            # size_str (and therefore self.value) are propertly aligned.
+            self.accurate_value = self.form.size
         else:
             aligned_sz = align_up(sz, self.form.alignment)
             aligned_sz_str = humanize_size(aligned_sz)
@@ -125,6 +129,7 @@ def lost_focus(self):
                         _("Rounded size up to {size}").format(size=aligned_sz_str),
                     )
                 )
+            self.accurate_value = aligned_sz
 
 
 class SizeField(FormField):
diff --git a/subiquity/ui/views/filesystem/tests/test_partition.py b/subiquity/ui/views/filesystem/tests/test_partition.py
index ab5363aa15..adb7e2832a 100644
--- a/subiquity/ui/views/filesystem/tests/test_partition.py
+++ b/subiquity/ui/views/filesystem/tests/test_partition.py
@@ -58,6 +58,7 @@ def test_create_partition(self):
         gap = gaps.Gap(device=disk, offset=1 << 20, size=99 << 30)
         view, stretchy = make_partition_view(model, disk, gap=gap)
         view_helpers.enter_data(stretchy.form, valid_data)
+        stretchy.form.size.widget.lost_focus()
         view_helpers.click(stretchy.form.done_btn.base_widget)
         valid_data["mount"] = "/"
         valid_data["size"] = dehumanize_size(valid_data["size"])
@@ -77,6 +78,7 @@ def test_edit_partition(self):
         view, stretchy = make_partition_view(model, disk, partition=partition)
         self.assertTrue(stretchy.form.done_btn.enabled)
         view_helpers.enter_data(stretchy.form, form_data)
+        stretchy.form.size.widget.lost_focus()
         view_helpers.click(stretchy.form.done_btn.base_widget)
         expected_data = {
             "size": dehumanize_size(form_data["size"]),
@@ -111,6 +113,7 @@ def test_edit_existing_partition(self):
         self.assertFalse(stretchy.form.size.enabled)
         self.assertTrue(stretchy.form.done_btn.enabled)
         view_helpers.enter_data(stretchy.form, form_data)
+        stretchy.form.size.widget.lost_focus()
         view_helpers.click(stretchy.form.done_btn.base_widget)
         expected_data = {
             "fstype": "xfs",
@@ -177,6 +180,7 @@ def test_edit_boot_partition(self):
         self.assertEqual(stretchy.form.mount.value, "/boot/efi")
 
         view_helpers.enter_data(stretchy.form, form_data)
+        stretchy.form.size.widget.lost_focus()
         view_helpers.click(stretchy.form.done_btn.base_widget)
         expected_data = {
             "size": dehumanize_size(form_data["size"]),
diff --git a/subiquitycore/ui/form.py b/subiquitycore/ui/form.py
index ea73c5887b..ad248dad52 100644
--- a/subiquitycore/ui/form.py
+++ b/subiquitycore/ui/form.py
@@ -531,7 +531,11 @@ def as_data(self):
         data = {}
         for field in self._fields:
             if field.enabled:
-                data[field.field.name] = field.value
+                accurate_value = getattr(field.widget, "accurate_value", None)
+                if accurate_value is not None:
+                    data[field.field.name] = accurate_value
+                else:
+                    data[field.field.name] = field.value
         return data