diff --git a/backends/GenerateC.hs b/backends/GenerateC.hs
index e451a92..08ff13d 100644
--- a/backends/GenerateC.hs
+++ b/backends/GenerateC.hs
@@ -160,7 +160,8 @@ generateC = generate cgenOps
 
 cgenTopLevel :: A.AST -> CGen ()
 cgenTopLevel s
-    =  do tell ["#include <tock_support_cif.h>\n"]
+    =  do tell ["#define occam_INT_size ", show cIntSize,"\n"]
+          tell ["#include <tock_support_cif.h>\n"]
           cs <- getCompState
           (tlpName, tlpChans) <- tlpInterface
           chans <- sequence [csmLift $ makeNonce "tlp_channel" | _ <- tlpChans]
diff --git a/backends/GenerateCPPCSP.hs b/backends/GenerateCPPCSP.hs
index cfc2b0f..cc5d31d 100644
--- a/backends/GenerateCPPCSP.hs
+++ b/backends/GenerateCPPCSP.hs
@@ -134,7 +134,8 @@ cppcspPrereq = cCppCommonPreReq ++ [Prop.allChansToAnyOrProtocol]
 -- | Generates the top-level code for an AST.
 cppgenTopLevel :: A.AST -> CGen ()
 cppgenTopLevel s
-    =  do tell ["#include <tock_support_cppcsp.h>\n"]
+    =  do tell ["#define occam_INT_size ", show cxxIntSize,"\n"]
+          tell ["#include <tock_support_cppcsp.h>\n"]
           --In future, these declarations could be moved to a header file:
           sequence_ $ map (call genForwardDeclaration) (listify (const True :: A.Specification -> Bool) s)
           call genStructured s (\m _ -> tell ["\n#error Invalid top-level item: ",show m])
diff --git a/rangetest.c b/rangetest.c
index 13cf55d..e26baf1 100644
--- a/rangetest.c
+++ b/rangetest.c
@@ -2,6 +2,7 @@ int g_stopped;
 
 #define occam_stop(pos, nargs, format, args...) do { g_stopped = 1; } while (0)
 
+#define occam_INT_size SIZEOF_INT
 #include "support/tock_support.h"
 
 #define report_failure(msg, args...) { printf(msg, ##args); }
diff --git a/support/tock_support.h b/support/tock_support.h
index 8346064..e5b5864 100644
--- a/support/tock_support.h
+++ b/support/tock_support.h
@@ -406,6 +406,85 @@ static inline double occam_DSQRT (double, const char *) occam_unused;
 static inline double occam_DSQRT (double v, const char *pos) {
 	return sqrt (v);
 }
+
+//We use #define so we can #undef afterwards
+#if occam_INT_size == 4
+	#define INT int32_t
+	#define UINT uint32_t
+#elif occam_INT_size == 8
+	#define INT int64_t
+	#define UINT uint64_t
+#else
+	#error You must define occam_INT_size when using this header
+#endif
+//Note that in the occam 2 manual, there is an error on page 104.
+//They say that range is the number of storable values in INTEGER,
+//their conceptual infinite type, so range would be infinity!
+//However, it is clear from the following lines that range is
+//the number of storable values in INT.
+
+#define occam_unsign(x) ((UINT)(x))
+#define occam_sign(x) ((INT)(x))
+
+static inline INT occam_LONGADD (INT, INT, INT, const char *) occam_unused;
+static inline INT occam_LONGADD (INT left, INT right, INT carry_in, const char *pos) {
+	if (left == __MAX(INT)) {
+		if (right == __MAX(INT)) {
+			occam_stop(pos, 3, "Overflow in LONGADD: %d + %d", left, right);
+		} else right += carry_in & 1;
+	} else left += carry_in & 1;
+
+	if (((right<1)&&(__MIN(INT)-right<=left)) || ((right>=1)&&(__MAX(INT)-right>=left))) {
+		return left + right;
+	} else {
+		occam_stop(pos, 3, "Overflow in LONGADD: %d + %d", left, right);
+	}
+}
+
+static inline INT occam_LONGSUM (INT, INT, INT, INT*, const char *) occam_unused;
+static inline INT occam_LONGSUM (INT left, INT right, INT carry_in, INT* result1, const char *pos) {
+	const UINT leftu = occam_unsign(left);
+	const UINT rightu = occam_unsign(right);
+	if (leftu == __MAX(UINT)) {
+		if (rightu == __MAX(UINT)) {
+			*result1 = -2;
+			return 1;
+		} else rightu += carry_in & 1;
+	} else leftu += carry_in & 1;
+
+	if (__MAX(UINT)-rightu>=leftu) {
+		*result1 = occam_sign(leftu + rightu);
+		return 0;
+	} else {
+		*result1 = occam_sign(leftu + rightu);
+		return 1;
+	}
+}
+
+static inline INT occam_NORMALISE (INT, INT, INT*, INT*,const char *) occam_unused;
+static inline INT occam_NORMALISE (INT hi_in, INT lo_in, INT* result1, INT* result2, const char *pos) {
+	if (hi_in == 0 && lo_in == 0) {
+		*result1 = *result2 = 0;
+		return 2*CHAR_BIT*sizeof(INT);
+	} else {
+		const INT highest_bit = __MIN(INT);
+		INT hi = hi_in;
+		INT lo = lo_in;
+		INT places = 0;
+		while ((hi & highest_bit) == 0) {
+			hi <<= 1;
+			hi |= (lo & highest_bit) >> ((CHAR_BIT*sizeof(INT))-1);
+			lo <<= 1;
+			places++;
+		}
+		*result1 = hi;
+		*result2 = lo;
+		return places;
+	}
+}
+#undef INT
+#undef UINT
+
 //}}}
 
 //{{{ Terminal handling