diff --git a/src/backends/meta-monitor-config-store.c b/src/backends/meta-monitor-config-store.c
index fe9406fd3..53a32cd2a 100644
--- a/src/backends/meta-monitor-config-store.c
+++ b/src/backends/meta-monitor-config-store.c
@@ -653,6 +653,7 @@ derive_logical_monitor_layout (MetaLogicalMonitorConfig    *logical_monitor_conf
   MetaMonitorConfig *monitor_config;
   int mode_width, mode_height;
   int width = 0, height = 0;
+  float scale;
   GList *l;
 
   monitor_config = logical_monitor_config->monitor_configs->data;
@@ -683,13 +684,21 @@ derive_logical_monitor_layout (MetaLogicalMonitorConfig    *logical_monitor_conf
       height = mode_height;
     }
 
+  scale = logical_monitor_config->scale;
+
   switch (layout_mode)
     {
     case META_LOGICAL_MONITOR_LAYOUT_MODE_LOGICAL:
-      width = roundf (width / logical_monitor_config->scale);
-      height = roundf (height / logical_monitor_config->scale);
+      width = roundf (width / scale);
+      height = roundf (height / scale);
       break;
     case META_LOGICAL_MONITOR_LAYOUT_MODE_PHYSICAL:
+      if (!G_APPROX_VALUE (scale, roundf (scale), FLT_EPSILON))
+        {
+          g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                       "A fractional scale with physical layout mode not allowed");
+          return FALSE;
+        }
       break;
     }