diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8a81b985b3..9f17ed40bb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -91,6 +91,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
   * Variables used as implicit fields in a record construction are now
     properly recognised as being used.
 
+  * futlib: the `num_bits` field for the integer modules in `math` now
+    have correct values.
+
 ## [0.2.0]
 
 ### Added
diff --git a/futlib/math.fut b/futlib/math.fut
index 13f6bfd05b..f98beea45a 100644
--- a/futlib/math.fut
+++ b/futlib/math.fut
@@ -261,7 +261,7 @@ module i16: (size with t = i16) = {
   let max (x: t) (y: t) = intrinsics.smax16 x y
   let min (x: t) (y: t) = intrinsics.smin16 x y
 
-  let num_bits = 8
+  let num_bits = 16
   let get_bit (bit: i32) (x: t) = to_i32 ((x >> i32 bit) & i32 1)
   let set_bit (bit: i32) (x: t) (b: i32) =
     ((x & i32 (intrinsics.~(1 intrinsics.<< b))) | x intrinsics.<< i32 b)
@@ -326,7 +326,7 @@ module i32: (size with t = i32) = {
   let max (x: t) (y: t) = intrinsics.smax32 x y
   let min (x: t) (y: t) = intrinsics.smin32 x y
 
-  let num_bits = 8
+  let num_bits = 32
   let get_bit (bit: i32) (x: t) = to_i32 ((x >> i32 bit) & i32 1)
   let set_bit (bit: i32) (x: t) (b: i32) =
     ((x & i32 (intrinsics.~(1 intrinsics.<< b))) | x intrinsics.<< i32 b)
@@ -391,7 +391,7 @@ module i64: (size with t = i64) = {
   let max (x: t) (y: t) = intrinsics.smax64 x y
   let min (x: t) (y: t) = intrinsics.smin64 x y
 
-  let num_bits = 8
+  let num_bits = 64
   let get_bit (bit: i32) (x: t) = to_i32 ((x >> i32 bit) & i32 1)
   let set_bit (bit: i32) (x: t) (b: i32) =
     ((x & i32 (intrinsics.~(1 intrinsics.<< b))) | x intrinsics.<< i32 b)
@@ -521,7 +521,7 @@ module u16: (size with t = u16) = {
   let max (x: t) (y: t) = unsign (intrinsics.umax16 (sign x) (sign y))
   let min (x: t) (y: t) = unsign (intrinsics.umin16 (sign x) (sign y))
 
-  let num_bits = 8
+  let num_bits = 16
   let get_bit (bit: i32) (x: t) = to_i32 ((x >> i32 bit) & i32 1)
   let set_bit (bit: i32) (x: t) (b: i32) =
     ((x & i32 (intrinsics.~(1 intrinsics.<< b))) | x intrinsics.<< i32 b)
@@ -586,7 +586,7 @@ module u32: (size with t = u32) = {
   let max (x: t) (y: t) = unsign (intrinsics.umax32 (sign x) (sign y))
   let min (x: t) (y: t) = unsign (intrinsics.umin32 (sign x) (sign y))
 
-  let num_bits = 8
+  let num_bits = 32
   let get_bit (bit: i32) (x: t) = to_i32 ((x >> i32 bit) & i32 1)
   let set_bit (bit: i32) (x: t) (b: i32) =
     ((x & i32 (intrinsics.~(1 intrinsics.<< b))) | x intrinsics.<< i32 b)
@@ -651,7 +651,7 @@ module u64: (size with t = u64) = {
   let max (x: t) (y: t) = unsign (intrinsics.umax64 (sign x) (sign y))
   let min (x: t) (y: t) = unsign (intrinsics.umin64 (sign x) (sign y))
 
-  let num_bits = 8
+  let num_bits = 64
   let get_bit (bit: i32) (x: t) = to_i32 ((x >> i32 bit) & i32 1)
   let set_bit (bit: i32) (x: t) (b: i32) =
     ((x & i32 (intrinsics.~(1 intrinsics.<< b))) | x intrinsics.<< i32 b)