diff --git a/fish-rust/src/common.rs b/fish-rust/src/common.rs
index 440856b49..b7e8739ba 100644
--- a/fish-rust/src/common.rs
+++ b/fish-rust/src/common.rs
@@ -1433,9 +1433,9 @@ fn can_be_encoded(wc: char) -> bool {
 
 /// Call read, blocking and repeating on EINTR. Exits on EAGAIN.
 /// \return the number of bytes read, or 0 on EOF. On EAGAIN, returns -1 if nothing was read.
-pub fn read_blocked(fd: RawFd, mut buf: &mut [u8]) -> isize {
+pub fn read_blocked(fd: RawFd, buf: &mut [u8]) -> isize {
     loop {
-        let res = unsafe { libc::read(fd, std::ptr::addr_of_mut!(buf).cast(), buf.len()) };
+        let res = unsafe { libc::read(fd, buf.as_mut_ptr().cast(), buf.len()) };
         if res < 0 && errno::errno().0 == EINTR {
             continue;
         }
diff --git a/tests/checks/math.fish b/tests/checks/math.fish
index 066a4a837..d191971ea 100644
--- a/tests/checks/math.fish
+++ b/tests/checks/math.fish
@@ -335,3 +335,6 @@ math 0x0_2.0_0_0P0_2
 # CHECK: 8
 math -0x8p-0_3
 # CHECK: -1
+
+echo 5 + 6 | math
+# CHECK: 11