diff --git a/src/fr/inrialpes/exmo/align/impl/method/SubsDistNameAlignment.java b/src/fr/inrialpes/exmo/align/impl/method/SubsDistNameAlignment.java
index 2cb9be6f8e192c07e0f534e76622ad7edc1bce2d..eb96bf67b15b7babed198d14362aaa55eca01ddd 100644
--- a/src/fr/inrialpes/exmo/align/impl/method/SubsDistNameAlignment.java
+++ b/src/fr/inrialpes/exmo/align/impl/method/SubsDistNameAlignment.java
@@ -52,17 +52,23 @@ public class SubsDistNameAlignment extends DistanceAlignment implements Alignmen
 		public double measure( OWLClass cl1, OWLClass cl2 ) throws OWLException{
 		    String s1 = cl1.getURI().getFragment();
 		    String s2 = cl2.getURI().getFragment();
-		    return StringDistances.subStringDistance(s1.toLowerCase(),s2.toLowerCase());
+		    if ( s1 != null && s2 != null )
+			return StringDistances.subStringDistance(s1.toLowerCase(),s2.toLowerCase());
+		    else return 1.;
 		}
 		public double measure( OWLProperty pr1, OWLProperty pr2 ) throws OWLException{
 		    String s1 = pr1.getURI().getFragment();
 		    String s2 = pr2.getURI().getFragment();
-		    return StringDistances.subStringDistance(s1.toLowerCase(),s2.toLowerCase());
+		    if ( s1 != null && s2 != null )
+			return StringDistances.subStringDistance(s1.toLowerCase(),s2.toLowerCase());
+		    else return 1.;
 		}
 		public double measure( OWLIndividual id1, OWLIndividual id2 ) throws OWLException{
 		    String s1 = id1.getURI().getFragment();
 		    String s2 = id2.getURI().getFragment();
-		    return StringDistances.subStringDistance(s1.toLowerCase(),s2.toLowerCase());
+		    if ( s1 != null && s2 != null )
+			return StringDistances.subStringDistance(s1.toLowerCase(),s2.toLowerCase());
+		    else return 1.;
 		}
 	    } );
 	setType("**");