diff --git a/src/lib_protocol_environment/sigs/v1/int32.mli b/src/lib_protocol_environment/sigs/v1/int32.mli
index eb0933726..4b85af947 100644
--- a/src/lib_protocol_environment/sigs/v1/int32.mli
+++ b/src/lib_protocol_environment/sigs/v1/int32.mli
@@ -15,7 +15,7 @@
 
 (* TEZOS CHANGES
 
-   * Import version 4.04.0
+   * Import version 4.06.1
    * Remove deprecated functions
 
 *)
@@ -91,7 +91,7 @@ external logxor : int32 -> int32 -> int32 = "%int32_xor"
 (** Bitwise logical exclusive or. *)
 
 val lognot : int32 -> int32
-(** Bitwise logical negation *)
+(** Bitwise logical negation. *)
 
 external shift_left : int32 -> int -> int32 = "%int32_lsl"
 (** [Int32.shift_left x y] shifts [x] to the left by [y] bits.
@@ -135,13 +135,26 @@ external to_float : int32 -> float
 
 external of_string : string -> int32 = "caml_int32_of_string"
 (** Convert the given string to a 32-bit integer.
-    The string is read in decimal (by default) or in hexadecimal,
-    octal or binary if the string begins with [0x], [0o] or [0b]
-    respectively.
-    Raise [Failure "int_of_string"] if the given string is not
+    The string is read in decimal (by default, or if the string
+    begins with [0u]) or in hexadecimal, octal or binary if the
+    string begins with [0x], [0o] or [0b] respectively.
+
+    The [0u] prefix reads the input as an unsigned integer in the range
+    [[0, 2*Int32.max_int+1]].  If the input exceeds {!Int32.max_int}
+    it is converted to the signed integer
+    [Int32.min_int + input - Int32.max_int - 1].
+
+    The [_] (underscore) character can appear anywhere in the string
+    and is ignored.
+    Raise [Failure "Int32.of_string"] if the given string is not
     a valid representation of an integer, or if the integer represented
     exceeds the range of integers representable in type [int32]. *)
 
+val of_string_opt: string -> int32 option
+(** Same as [of_string], but return [None] instead of raising.
+    @since 4.05 *)
+
+
 val to_string : int32 -> string
 (** Return the string representation of its argument, in signed decimal. *)
 
@@ -173,4 +186,3 @@ val compare: t -> t -> int
 val equal: t -> t -> bool
 (** The equal function for int32s.
     @since 4.03.0 *)
-