diff --git a/tfprng.c b/tfprng.c
index 5022857..f83963c 100644
--- a/tfprng.c
+++ b/tfprng.c
@@ -85,7 +85,7 @@ TFNG_UNIT_TYPE tfng_prng_range_r(void *sdata, TFNG_UNIT_TYPE s, TFNG_UNIT_TYPE d
 {
 	TFNG_UNIT_TYPE c = tfng_prng_random_r(sdata);
 	if (d <= s) return s;
-	return s + c / ((TFNG_UNIT_TYPE)~0 / (d - s + 1) + 1);
+	return TFNG_PRNG_RANGE(c, TFNG_UNIT_TYPE, s, d);
 }
 
 TFNG_UNIT_TYPE tfng_prng_range(TFNG_UNIT_TYPE s, TFNG_UNIT_TYPE d)
diff --git a/tfprng.h b/tfprng.h
index f7d3b3f..15880b7 100644
--- a/tfprng.h
+++ b/tfprng.h
@@ -6,6 +6,7 @@
 
 #define TFNG_PRNG_KEY_SIZE TFNG_KEY_SIZE
 #define TFNG_PRNG_SIZE_UNIT TFNG_SIZE_UNIT
+#define TFNG_PRNG_RANGE(C, T, S, D) (S + C / ((T)~0 / (D - S + 1) + 1))
 
 size_t tfng_prng_datasize(void);
 void tfng_prng_seedkey_r(void *sdata, const void *skey);