diff --git a/GenerateCPPCSP.hs b/GenerateCPPCSP.hs
index af6d0fc..22cc759 100644
--- a/GenerateCPPCSP.hs
+++ b/GenerateCPPCSP.hs
@@ -336,7 +336,7 @@ genCPPCSPTime ops e
           tell ["unsigned ",curTimeLow," = (unsigned)remainder(1000000.0 * ",curTime,",4294967296.0);"]
           tell ["unsigned ",curTimeHigh," = (unsigned)((1000000.0 * ",curTime,") / 4294967296.0);"]
           --if time is less than curTime, it must have wrapped around so add one:
-          tell ["csp::Time ",retTime," = csp::Seconds((((double)(",curTimeHigh," + (",time," < ",curTimeLow, " ? 1 : 0)) * 4294967296.0) + (double)",time,") / 1000000.0);"]
+          tell ["csp::Time ",retTime," = csp::Seconds((((double)(",curTimeHigh," + TimeDiffHelper(",curTimeLow,",",time,")) * 4294967296.0) + (double)",time,") / 1000000.0);"]
           return retTime
 
 cppgenTimerWait :: GenOps -> A.Expression -> CGen ()
diff --git a/tock_support_cppcsp.h b/tock_support_cppcsp.h
index bd3129f..471772e 100644
--- a/tock_support_cppcsp.h
+++ b/tock_support_cppcsp.h
@@ -35,6 +35,35 @@ public:
 #include <boost/preprocessor/repetition/repeat.hpp>
 #include <boost/preprocessor/repetition/repeat_from_to.hpp>
 
+inline unsigned TimeDiffHelper(unsigned now,unsigned waitFor)
+{
+	//If waitFor is in the 2^31 before now, it is in the past:
+	if (now - waitFor < 2147483648)
+	{
+		//if we have wrapped round between waitFor and now, we actually want to return a minus-one:
+		if ((waitFor >= 2147483648) && (now < 2147483648))
+		{
+			return (unsigned)(int)(-1);
+		}
+		else
+		{
+			return 0;
+		}
+	}
+	else
+	{
+		//It is in the future.  If we will wrap round before getting there, return one:
+		if ((now >= 2147483648) && (waitFor < 2147483648))
+		{
+			return 1;
+		}
+		else
+		{
+			return 0;
+		}
+	}
+}
+
 class StreamWriter : public csp::CSProcess
 {
 private: