diff --git a/pkg/storaged/dialog.jsx b/pkg/storaged/dialog.jsx
index 927a5db28151..ad25cefee462 100644
--- a/pkg/storaged/dialog.jsx
+++ b/pkg/storaged/dialog.jsx
@@ -943,7 +943,7 @@ class SizeSliderElement extends React.Component {
         const { unit } = this.state;
 
         const change_slider = (_event, f) => {
-            onChange(Math.max(min, size_slider_round(f * max / 100, round)));
+            onChange(Math.max(min, size_slider_round(f, round)));
         };
 
         const change_text = (value) => {
@@ -972,7 +972,8 @@ class SizeSliderElement extends React.Component {
         return (
             <Grid hasGutter className="size-slider">
                 <GridItem span={12} sm={8}>
-                    <Slider showBoundaries={false} value={(slider_val / max) * 100} onChange={change_slider} />
+                    <Slider showBoundaries={false} min={min} max={max} step={(max - min) / 500}
+                            value={slider_val} onChange={change_slider} />
                 </GridItem>
                 <GridItem span={6} sm={2}>
                     <TextInputPF4 className="size-text" value={text_val} onChange={(_event, value) => change_text(value)} />
diff --git a/test/verify/check-storage-partitions b/test/verify/check-storage-partitions
index c15bdb3a7fe8..81535fa86d9a 100755
--- a/test/verify/check-storage-partitions
+++ b/test/verify/check-storage-partitions
@@ -85,22 +85,27 @@ class TestStoragePartitions(storagelib.StorageCase):
         about_half_way = width / 2 + 1
 
         b.mouse(slider, "click", about_half_way, 0)
-        self.dialog_wait_val("size", 27.3)
+        self.dialog_wait_val("size", 27.4)
         b.focus(slider + " + .pf-v5-c-slider__thumb")
         b.key_press(chr(37), use_ord=True)  # arrow left
-        self.dialog_wait_val("size", 26.7)
+        b.key_press(chr(37), use_ord=True)
+        b.key_press(chr(37), use_ord=True)
+        self.dialog_wait_val("size", 27.1)
 
         # Check that changing units affects the text input
         unit = "1000000000"
         b.select_from_dropdown(".size-unit > select", unit)
-        self.dialog_wait_val("size", "0.0267", unit)
+        self.dialog_wait_val("size", "0.0271", unit)
 
         self.dialog_apply()
         self.dialog_wait_close()
 
-        # With old Udisks2 versions, the partition will end up being
-        # 25.1M while newer versions give us 26M or 25M.
-        testlib.wait(lambda: m.execute(f"lsblk -no SIZE {disk}1").strip() in ["25M", "25.1M", "26M"])
+        # 27.1 MB is about 25.84 MiB. Some versions of
+        # UDisks2/libblockdev/libparted/... round this up to 26 MiB
+        # when creating the partition, some (newer ones) round it down
+        # to 25 MiB.
+        #
+        testlib.wait(lambda: m.execute(f"lsblk -no SIZE {disk}1").strip() in ["26M", "25M"])
 
     def testResize(self):
         m = self.machine