diff --git a/src/validators/schema/TraverseSchema.cpp b/src/validators/schema/TraverseSchema.cpp
index 5ad30bca3efcd9c453244d1f0e5c9eb13f8abe93..151ac27812038c941fb55f99189bb6dd16ee7023 100644
--- a/src/validators/schema/TraverseSchema.cpp
+++ b/src/validators/schema/TraverseSchema.cpp
@@ -3933,7 +3933,7 @@ bool TraverseSchema::traverseIdentityConstraint(IdentityConstraint* const ic,
         if (chOffset == -1)
             break;
 
-        fBuffer.append(xpathExpr + startIndex, chOffset + 1);
+        fBuffer.append(xpathExpr + startIndex, chOffset + 1 - startIndex);
         startIndex = chOffset + 1;    
     }