diff --git a/src/test/ns3tcp/ns3tcp-interop-test-suite.cc b/src/test/ns3tcp/ns3tcp-interop-test-suite.cc
index 20dd7106e..12512e1e4 100644
--- a/src/test/ns3tcp/ns3tcp-interop-test-suite.cc
+++ b/src/test/ns3tcp/ns3tcp-interop-test-suite.cc
@@ -16,6 +16,8 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  */
 
+#include <string>
+
 #include "ns3/log.h"
 #include "ns3/abort.h"
 #include "ns3/test.h"
@@ -110,7 +112,8 @@ Ns3TcpInteroperabilityTestCase::DoSetup (void)
   // We expect there to be a file called tcp-interop-response-vectors.pcap in
   // response-vectors/ of this directory
   //
-  m_pcapFilename = NS_TEST_SOURCEDIR + "/response-vectors/ns3tcp-interop-response-vectors.pcap";
+  m_pcapFilename = static_cast<std::string> (NS_TEST_SOURCEDIR) + 
+    static_cast<std::string> ("/response-vectors/ns3tcp-interop-response-vectors.pcap");
 
   if (m_writeVectors)
     {
diff --git a/src/test/ns3tcp/ns3tcp-state-test-suite.cc b/src/test/ns3tcp/ns3tcp-state-test-suite.cc
index b141dfc36..938c8509e 100644
--- a/src/test/ns3tcp/ns3tcp-state-test-suite.cc
+++ b/src/test/ns3tcp/ns3tcp-state-test-suite.cc
@@ -17,6 +17,7 @@
  */
 
 #include <iomanip>
+#include <string>
 
 #include "ns3/log.h"
 #include "ns3/abort.h"
@@ -116,7 +117,7 @@ Ns3TcpStateTestCase::DoSetup (void)
   //
   std::ostringstream oss;
   oss << "/response-vectors/ns3tcp-state" << m_testCase << "-response-vectors.pcap";
-  m_pcapFilename = NS_TEST_SOURCEDIR + oss.str ();
+  m_pcapFilename = static_cast<std::string> (NS_TEST_SOURCEDIR) + oss.str ();
 
   if (m_writeVectors)
     {