diff --git a/rust-version b/rust-version
index 5d44fe9e4b8..0260e9beab1 100644
--- a/rust-version
+++ b/rust-version
@@ -1 +1 @@
-bf469eb6c20ccea05400a1942c70343f36705e1c
+172acf8f61018df3719e42e633ffd62ebecaa1e7
diff --git a/src/shims/posix/fs.rs b/src/shims/posix/fs.rs
index 50589ca322d..10f0c910979 100644
--- a/src/shims/posix/fs.rs
+++ b/src/shims/posix/fs.rs
@@ -831,17 +831,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         };
 
         let path = this.read_path_from_c_str(pathname_scalar)?.into_owned();
-        // `flags` should be a `c_int` but the `syscall` function provides an `isize`.
-        let flags: i32 =
-            this.read_scalar(flags_op)?.to_machine_isize(&*this.tcx)?.try_into().map_err(|e| {
-                err_unsup_format!("failed to convert pointer sized operand to integer: {}", e)
-            })?;
+        // See <https://github.com/rust-lang/rust/pull/79196> for a discussion of argument sizes.
+        let flags = this.read_scalar(flags_op)?.to_i32()?;
         let empty_path_flag = flags & this.eval_libc("AT_EMPTY_PATH")?.to_i32()? != 0;
-        // `dirfd` should be a `c_int` but the `syscall` function provides an `isize`.
-        let dirfd: i32 =
-            this.read_scalar(dirfd_op)?.to_machine_isize(&*this.tcx)?.try_into().map_err(|e| {
-                err_unsup_format!("failed to convert pointer sized operand to integer: {}", e)
-            })?;
+        let dirfd = this.read_scalar(dirfd_op)?.to_i32()?;
         // We only support:
         // * interpreting `path` as an absolute directory,
         // * interpreting `path` as a path relative to `dirfd` when the latter is `AT_FDCWD`, or
diff --git a/src/shims/posix/linux/foreign_items.rs b/src/shims/posix/linux/foreign_items.rs
index 23dc02a6aff..45afbd05efc 100644
--- a/src/shims/posix/linux/foreign_items.rs
+++ b/src/shims/posix/linux/foreign_items.rs
@@ -208,9 +208,8 @@ fn getrandom<'tcx>(
 
     // The only supported flags are GRND_RANDOM and GRND_NONBLOCK,
     // neither of which have any effect on our current PRNG.
-    let _flags = this.read_scalar(flags)?;
-    // FIXME: Check that this is an integer type of the right size.
-    // Currently, some callers pass i32 and some usize, is that even allowed?
+    // See <https://github.com/rust-lang/rust/pull/79196> for a discussion of argument sizes.
+    let _flags = this.read_scalar(flags)?.to_i32();
 
     this.gen_random(ptr, len)?;
     this.write_scalar(Scalar::from_machine_usize(len, this), dest)?;