Index: trunk/src/org/openstreetmap/josm/data/projection/proj/AbstractProj.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/projection/proj/AbstractProj.java	(revision 18342)
+++ trunk/src/org/openstreetmap/josm/data/projection/proj/AbstractProj.java	(revision 18353)
@@ -5,4 +5,5 @@
 import org.openstreetmap.josm.data.projection.ProjectionConfigurationException;
 import org.openstreetmap.josm.tools.CheckParameterUtil;
+import org.openstreetmap.josm.tools.Logging;
 
 /**
@@ -170,4 +171,8 @@
     // Iteratively solve equation (7-9) from Snyder.
     final double cphi2(final double ts) {
+        if (Double.isNaN(ts)) {
+            Logging.warn("Trying to project invalid NaN coordinates");
+            return Double.NaN;
+        }
         final double eccnth = 0.5 * e;
         double phi = (Math.PI/2) - 2.0 * Math.atan(ts);