diff --git a/src/headform.c b/src/headform.c
--- a/src/headform.c
+++ b/src/headform.c
@@ -39,1 +39,8 @@
+/* The output-management protocol transmits scale as a Wayland 24.8 fixed
+ * point value. Use that same value for preview geometry so a fractional scale
+ * cannot change underneath positions during the first apply. */
+static double canonicalize_scale(double scale) {
+  return wl_fixed_to_double(wl_fixed_from_double(scale));
+}
+
 static void head_form_update_sensitivity(WdHeadForm *form) {
@@ -359,2 +366,3 @@ void wd_head_form_fill_config(WdHeadForm *form, struct wd_head_config *output) {
-  output->scale = gtk_spin_button_get_value(GTK_SPIN_BUTTON(priv->scale));
+  output->scale = canonicalize_scale(
+      gtk_spin_button_get_value(GTK_SPIN_BUTTON(priv->scale)));
   output->x = gtk_spin_button_get_value(GTK_SPIN_BUTTON(priv->pos_x));
@@ -385,2 +393,3 @@ void wd_head_form_get_dimensions(WdHeadForm *form, WdHeadDimensions *dimensions)
-  dimensions->scale = gtk_spin_button_get_value(GTK_SPIN_BUTTON(priv->scale));
+  dimensions->scale = canonicalize_scale(
+      gtk_spin_button_get_value(GTK_SPIN_BUTTON(priv->scale)));
   dimensions->rotation_id = g_variant_get_int32(g_action_get_state(priv->rotate_action)) / 90;