diff --git a/topcat/src/main/uk/ac/starlink/topcat/plot2/SkyPlotWindow.java b/topcat/src/main/uk/ac/starlink/topcat/plot2/SkyPlotWindow.java
index 070f80b612..2d5d4c5e36 100644
--- a/topcat/src/main/uk/ac/starlink/topcat/plot2/SkyPlotWindow.java
+++ b/topcat/src/main/uk/ac/starlink/topcat/plot2/SkyPlotWindow.java
@@ -18,6 +18,7 @@
 import uk.ac.starlink.ttools.plot2.config.ConfigKey;
 import uk.ac.starlink.ttools.plot2.config.ConfigMeta;
 import uk.ac.starlink.ttools.plot2.config.Specifier;
+import uk.ac.starlink.ttools.plot2.config.SkySysConfigKey;
 import uk.ac.starlink.ttools.plot2.geom.SkyAspect;
 import uk.ac.starlink.ttools.plot2.geom.SkyDataGeom;
 import uk.ac.starlink.ttools.plot2.geom.SkyPlotType;
@@ -34,8 +35,8 @@ public class SkyPlotWindow
        extends StackPlotWindow<SkySurfaceFactory.Profile,SkyAspect> {
     private static final SkyPlotType PLOT_TYPE = SkyPlotType.getInstance();
     private static final ConfigKey<SkySys> DATASYS_KEY =
-        SkySys.createConfigKey( new ConfigMeta( "datasys", "Data Sky System" ),
-                                false );
+        new SkySysConfigKey( new ConfigMeta( "datasys", "Data Sky System" ),
+                             false );
 
     /**
      * Constructor.
diff --git a/ttools/src/main/uk/ac/starlink/ttools/plot2/geom/SkySys.java b/ttools/src/main/uk/ac/starlink/ttools/plot2/geom/SkySys.java
index 9f3e93579f..7b88840472 100644
--- a/ttools/src/main/uk/ac/starlink/ttools/plot2/geom/SkySys.java
+++ b/ttools/src/main/uk/ac/starlink/ttools/plot2/geom/SkySys.java
@@ -4,9 +4,6 @@
 import uk.ac.starlink.table.ValueInfo;
 import uk.ac.starlink.ttools.plot.Matrices;
 import uk.ac.starlink.ttools.plot2.PlotUtil;
-import uk.ac.starlink.ttools.plot2.config.ConfigKey;
-import uk.ac.starlink.ttools.plot2.config.ConfigMeta;
-import uk.ac.starlink.ttools.plot2.config.OptionConfigKey;
 
 /**
  * Sky coordinate system definition.
@@ -261,25 +258,4 @@ public static SkySys[] getKnownSystems( boolean includeNull ) {
                                                  : new SkySys[ 0 ],
                                      KNOWN_SYSTEMS );
     }
-
-    /**
-     * Creates a config key for choosing a sky system.
-     *
-     * @param  meta  config key metadata
-     * @param  includeNull  true iff null is a permitted option
-     * @return  sky system config key
-     */
-    public static ConfigKey<SkySys> createConfigKey( ConfigMeta meta,
-                                                     boolean includeNull ) {
-        return new OptionConfigKey<SkySys>( meta, SkySys.class,
-                                            getKnownSystems( includeNull ) ) {
-            public String valueToString( SkySys sys ) {
-                return sys == null ? "generic" : super.valueToString( sys );
-            }
-            public SkySys stringToValue( String str ) {
-                return "generic".equals( str ) ? null
-                                               : super.stringToValue( str );
-            }
-        };
-    }
 }