diff --git a/src/opcode.rs b/src/opcode.rs
index 6fe5b348..05cb62d7 100644
--- a/src/opcode.rs
+++ b/src/opcode.rs
@@ -1482,6 +1482,9 @@ opcode! {
         fd: { impl sealed::UseFixed },
         cmd_op: { u32 },
         ;;
+        /// The `buf_index` is an index into an array of fixed buffers,
+        /// and is only valid if fixed buffers were registered.
+        buf_index: Option<u16> = None,
         /// Arbitrary command data.
         cmd: [u8; 16] = [0u8; 16]
     }
@@ -1489,13 +1492,19 @@ opcode! {
     pub const CODE = sys::IORING_OP_URING_CMD;
 
     pub fn build(self) -> Entry {
-        let UringCmd16 { fd, cmd_op, cmd } = self;
+        let UringCmd16 { fd, cmd_op, cmd, buf_index } = self;
 
         let mut sqe = sqe_zeroed();
         sqe.opcode = Self::CODE;
         assign_fd!(sqe.fd = fd);
         sqe.__bindgen_anon_1.__bindgen_anon_1.cmd_op = cmd_op;
         unsafe { *sqe.__bindgen_anon_6.cmd.as_mut().as_mut_ptr().cast::<[u8; 16]>() = cmd };
+        if let Some(buf_index) = buf_index {
+            sqe.__bindgen_anon_4.buf_index = buf_index;
+            unsafe {
+                sqe.__bindgen_anon_3.uring_cmd_flags |= sys::IORING_URING_CMD_FIXED;
+            }
+        }
         Entry(sqe)
     }
 }
@@ -1506,6 +1515,9 @@ opcode! {
         fd: { impl sealed::UseFixed },
         cmd_op: { u32 },
         ;;
+        /// The `buf_index` is an index into an array of fixed buffers,
+        /// and is only valid if fixed buffers were registered.
+        buf_index: Option<u16> = None,
         /// Arbitrary command data.
         cmd: [u8; 80] = [0u8; 80]
     }
@@ -1513,7 +1525,7 @@ opcode! {
     pub const CODE = sys::IORING_OP_URING_CMD;
 
     pub fn build(self) -> Entry128 {
-        let UringCmd80 { fd, cmd_op, cmd } = self;
+        let UringCmd80 { fd, cmd_op, cmd, buf_index } = self;
 
         let cmd1 = cmd[..16].try_into().unwrap();
         let cmd2 = cmd[16..].try_into().unwrap();
@@ -1523,6 +1535,12 @@ opcode! {
         assign_fd!(sqe.fd = fd);
         sqe.__bindgen_anon_1.__bindgen_anon_1.cmd_op = cmd_op;
         unsafe { *sqe.__bindgen_anon_6.cmd.as_mut().as_mut_ptr().cast::<[u8; 16]>() = cmd1 };
+        if let Some(buf_index) = buf_index {
+            sqe.__bindgen_anon_4.buf_index = buf_index;
+            unsafe {
+                sqe.__bindgen_anon_3.uring_cmd_flags |= sys::IORING_URING_CMD_FIXED;
+            }
+        }
         Entry128(Entry(sqe), cmd2)
     }
 }