diff --git a/ZString.cpp b/ZString.cpp
index e7ac35e..e6f1445 100644
--- a/ZString.cpp
+++ b/ZString.cpp
@@ -171,6 +171,13 @@ namespace coreutils {
    }
    
    ZString ZString::substring(int start, int len) {
+      char *end = data + length;
+      char *startChar = data + start;
+      char *endChar = startChar + len;
+      char newlen = endChar > end ? endChar - end: len;
+      if(startChar < end) {
+	 return ZString(startChar, newlen);
+      }
       return ZString();
    }   
    
diff --git a/testing/zstring_test.cpp b/testing/zstring_test.cpp
index 904bacb..3e1d978 100644
--- a/testing/zstring_test.cpp
+++ b/testing/zstring_test.cpp
@@ -85,6 +85,11 @@ int main(int argc, char **argv) {
    coreutils::ZString test14("25.5");
    coreutils::ZString test15("xyx");
    std::cout << test14.startsWithDouble() << ":" << test15.startsWithDouble() << std::endl;
-   
+
+   coreutils::ZString test16("This is a test of substring");
+   std::cout << test16.substring(10) << std::endl;
+   std::cout << test16.substring(10, 4) << std::endl;
+   std::cout << test16.substring(0, 7) << std::endl;
+   std::cout << test16.substring(18, 20) << std::endl;
    
 }