diff --git a/tests/soak-peer-client.cpp b/tests/soak-peer-client.cpp
index 172332c..1a870dc 100644
--- a/tests/soak-peer-client.cpp
+++ b/tests/soak-peer-client.cpp
@@ -320,7 +320,7 @@ static HRESULT CALLBACK callback(PVOID pvUserContext, DWORD dwMessageType, PVOID
 				*now_p = now;
 				
 				DPNHANDLE s_handle;
-				HRESULT res = instance->SendTo(cp->dpnidPlayer, &bd, 1, 0, now_p, &s_handle, 0);
+				HRESULT res = instance->SendTo(cp->dpnidPlayer, &bd, 1, 0, now_p, &s_handle, DPNSEND_GUARANTEED);
 				if(res != DPNSUCCESS_PENDING)
 				{
 					timed_fprintf(stderr, "IDirectPlay8Peer::SendTo() failed with HRESULT %08x", (unsigned int)(res));
@@ -389,7 +389,7 @@ static HRESULT CALLBACK callback(PVOID pvUserContext, DWORD dwMessageType, PVOID
 				*now_p = now;
 				
 				DPNHANDLE s_handle;
-				HRESULT res = instance->SendTo(r->dpnidSender, &bd, 1, 0, now_p, &s_handle, 0);
+				HRESULT res = instance->SendTo(r->dpnidSender, &bd, 1, 0, now_p, &s_handle, DPNSEND_GUARANTEED);
 				if(res != DPNSUCCESS_PENDING)
 				{
 					timed_fprintf(stderr, "IDirectPlay8Peer::SendTo() failed with HRESULT %08x", (unsigned int)(res));
diff --git a/tests/soak-peer-server.cpp b/tests/soak-peer-server.cpp
index 61e12f1..209a385 100644
--- a/tests/soak-peer-server.cpp
+++ b/tests/soak-peer-server.cpp
@@ -206,7 +206,7 @@ static HRESULT CALLBACK callback(PVOID pvUserContext, DWORD dwMessageType, PVOID
 			DPN_BUFFER_DESC bd = { r->dwReceiveDataSize, r->pReceiveData };
 			
 			DPNHANDLE s_handle;
-			HRESULT res = instance->SendTo(r->dpnidSender, &bd, 1, 0, NULL, &s_handle, 0);
+			HRESULT res = instance->SendTo(r->dpnidSender, &bd, 1, 0, NULL, &s_handle, DPNSEND_GUARANTEED);
 			if(res != DPNSUCCESS_PENDING)
 			{
 				fprintf(stderr, "IDirectPlay8Peer::SendTo() failed with HRESULT %08x\n", (unsigned int)(res));