diff --git a/Source/cmCTest.h b/Source/cmCTest.h
index c51a112fa..44a4c13f1 100644
--- a/Source/cmCTest.h
+++ b/Source/cmCTest.h
@@ -393,6 +393,10 @@ public:
 
 inline std::ostream& operator<< (std::ostream& os, const cmCTestLogWrite& c)
 {
+  if (!c.Length)
+    {
+    return os;
+    }
   os.write(c.Data, c.Length);
   os.flush();
   return os;