diff --git a/src/runtime/src/rpc.rs b/src/runtime/src/rpc.rs
index bb17f507..beaab895 100644
--- a/src/runtime/src/rpc.rs
+++ b/src/runtime/src/rpc.rs
@@ -14,15 +14,20 @@ use crate::proto_core_io::ProtoWrite;
 use crate::proto_async;
 use self::tag::{Tag, TagIterator, split_tag};
 
+#[inline]
+fn alignment_offset(alignment: isize, ptr: isize) -> isize {
+    (alignment - ptr % alignment) % alignment
+}
+
 unsafe fn align_ptr<T>(ptr: *const ()) -> *const T {
     let alignment = core::mem::align_of::<T>() as isize;
-    let fix = (alignment - (ptr as isize) % alignment) % alignment;
+    let fix = alignment_offset(alignment, ptr as isize);
     ((ptr as isize) + fix) as *const T
 }
 
 unsafe fn align_ptr_mut<T>(ptr: *mut ()) -> *mut T {
     let alignment = core::mem::align_of::<T>() as isize;
-    let fix = (alignment - (ptr as isize) % alignment) % alignment;
+    let fix = alignment_offset(alignment, ptr as isize);
     ((ptr as isize) + fix) as *mut T
 }
 
@@ -66,6 +71,7 @@ async unsafe fn recv_value<F>(stream: &TcpStream, tag: Tag<'async_recursion>, da
             })
         }
         Tag::Tuple(it, arity) => {
+            *data = (*data).offset(alignment_offset(tag.alignment() as isize, *data as isize));
             let mut it = it.clone();
             for _ in 0..arity {
                 let tag = it.next().expect("truncated tag");
@@ -80,17 +86,24 @@ async unsafe fn recv_value<F>(stream: &TcpStream, tag: Tag<'async_recursion>, da
                 let length = proto_async::read_i32(stream).await? as usize;
                 (*ptr).length  = length as u32;
                 let tag = it.clone().next().expect("truncated tag");
-                let mut data = alloc(tag.size() * length as usize).await;
+                let data_size = tag.size() * length as usize +
+                    match tag {
+                        Tag::Int64 | Tag::Float64 => 4,
+                        _ => 0
+                    };
+                let mut data = alloc(data_size).await;
 
+                let alignment = tag.alignment();
+                data = data.offset(alignment_offset(alignment as isize, data as isize));
                 (*ptr).elements = data;
                 match tag {
                     Tag::Bool => {
-                        let ptr = align_ptr_mut::<u8>(data);
+                        let ptr = data as *mut u8;
                         let dest = core::slice::from_raw_parts_mut(ptr, length);
                         proto_async::read_chunk(stream, dest).await?;
                     },
                     Tag::Int32 => {
-                        let ptr = align_ptr_mut::<u32>(data);
+                        let ptr = data as *mut u32;
                         // reading as raw bytes and do endianness conversion later
                         let dest = core::slice::from_raw_parts_mut(ptr as *mut u8, length * 4);
                         proto_async::read_chunk(stream, dest).await?;
@@ -99,7 +112,7 @@ async unsafe fn recv_value<F>(stream: &TcpStream, tag: Tag<'async_recursion>, da
                         NativeEndian::from_slice_u32(dest);
                     },
                     Tag::Int64 | Tag::Float64 => {
-                        let ptr = align_ptr_mut::<u64>(data);
+                        let ptr = data as *mut u64;
                         let dest = core::slice::from_raw_parts_mut(ptr as *mut u8, length * 8);
                         proto_async::read_chunk(stream, dest).await?;
                         drop(dest);
@@ -125,18 +138,25 @@ async unsafe fn recv_value<F>(stream: &TcpStream, tag: Tag<'async_recursion>, da
                 }
 
                 let elt_tag = it.clone().next().expect("truncated tag");
-                *buffer = alloc(elt_tag.size() * total_len as usize).await;
+                let data_size = elt_tag.size() * total_len as usize +
+                    match elt_tag {
+                        Tag::Int64 | Tag::Float64 => 4,
+                        _ => 0
+                    };
+                let mut data = alloc(data_size).await;
 
+                let alignment = tag.alignment();
+                data = data.offset(alignment_offset(alignment as isize, data as isize));
+                *buffer = data;
                 let length = total_len as usize;
-                let mut data = *buffer;
                 match elt_tag {
                     Tag::Bool => {
-                        let ptr = align_ptr_mut::<u8>(data);
+                        let ptr = data as *mut u8;
                         let dest = core::slice::from_raw_parts_mut(ptr, length);
                         proto_async::read_chunk(stream, dest).await?;
                     },
                     Tag::Int32 => {
-                        let ptr = align_ptr_mut::<u32>(data);
+                        let ptr = data as *mut u32;
                         let dest = core::slice::from_raw_parts_mut(ptr as *mut u8, length * 4);
                         proto_async::read_chunk(stream, dest).await?;
                         drop(dest);
@@ -144,7 +164,7 @@ async unsafe fn recv_value<F>(stream: &TcpStream, tag: Tag<'async_recursion>, da
                         NativeEndian::from_slice_u32(dest);
                     },
                     Tag::Int64 | Tag::Float64 => {
-                        let ptr = align_ptr_mut::<u64>(data);
+                        let ptr = data as *mut u64;
                         let dest = core::slice::from_raw_parts_mut(ptr as *mut u8, length * 8);
                         proto_async::read_chunk(stream, dest).await?;
                         drop(dest);
@@ -161,6 +181,7 @@ async unsafe fn recv_value<F>(stream: &TcpStream, tag: Tag<'async_recursion>, da
             })
         }
         Tag::Range(it) => {
+            *data = (*data).offset(alignment_offset(tag.alignment() as isize, *data as isize));
             let tag = it.clone().next().expect("truncated tag");
             recv_value(stream, tag, data, alloc).await?;
             recv_value(stream, tag, data, alloc).await?;
@@ -407,7 +428,35 @@ mod tag {
             }
         }
 
+        pub fn alignment(self) -> usize {
+            use cslice::CSlice;
+            match self {
+                Tag::None => 1,
+                Tag::Bool => core::mem::align_of::<u8>(),
+                Tag::Int32 => core::mem::align_of::<i32>(),
+                Tag::Int64 => core::mem::align_of::<i64>(),
+                Tag::Float64 => core::mem::align_of::<f64>(),
+                // struct type: align to largest element
+                Tag::Tuple(it, arity) => {
+                    let it = it.clone();
+                    it.take(arity.into()).map(|t| t.alignment()).max().unwrap()
+                },
+                Tag::Range(it) => {
+                    let it = it.clone();
+                    it.take(3).map(|t| t.alignment()).max().unwrap()
+                }
+                // CSlice basically
+                Tag::Bytes | Tag::String | Tag::ByteArray | Tag::List(_) =>
+                    core::mem::align_of::<CSlice<()>>(),
+                // array buffer is allocated, so no need for alignment first
+                Tag::Array(_, _) => 1,
+                // will not be sent from the host
+                _ => unreachable!("unexpected tag from host")
+            }
+        }
+
         pub fn size(self) -> usize {
+            use super::alignment_offset;
             match self {
                 Tag::None => 0,
                 Tag::Bool => 1,
@@ -423,6 +472,8 @@ mod tag {
                     for _ in 0..arity {
                         let tag = it.next().expect("truncated tag");
                         size += tag.size();
+                        // includes padding
+                        size += alignment_offset(tag.alignment() as isize, size as isize) as usize;
                     }
                     size
                 }
@@ -445,10 +496,23 @@ mod tag {
 
     impl<'a> TagIterator<'a> {
         pub fn new(data: &'a [u8]) -> TagIterator<'a> {
-            TagIterator { data: data }
+            TagIterator { data }
         }
 
-        pub fn next(&mut self) -> Option<Tag<'a>> {
+
+        fn sub(&mut self, count: u8) -> TagIterator<'a> {
+            let data = self.data;
+            for _ in 0..count {
+                self.next().expect("truncated tag");
+            }
+            TagIterator { data: &data[..(data.len() - self.data.len())] }
+        }
+    }
+
+    impl<'a> core::iter::Iterator for TagIterator<'a> {
+        type Item = Tag<'a>;
+
+        fn next(&mut self) -> Option<Tag<'a>> {
             if self.data.len() == 0 {
                 return None
             }
@@ -481,14 +545,6 @@ mod tag {
                 _    => unreachable!()
             })
         }
-
-        fn sub(&mut self, count: u8) -> TagIterator<'a> {
-            let data = self.data;
-            for _ in 0..count {
-                self.next().expect("truncated tag");
-            }
-            TagIterator { data: &data[..(data.len() - self.data.len())] }
-        }
     }
 
     impl<'a> fmt::Display for TagIterator<'a> {