diff --git a/crates/generate/src/types.rs b/crates/generate/src/types.rs
index c5185a51a8..13338769e8 100644
--- a/crates/generate/src/types.rs
+++ b/crates/generate/src/types.rs
@@ -153,13 +153,19 @@ pub fn struct_is_copy(s: &witx::StructDatatype) -> bool {
 
 fn define_copy_struct(names: &Names, name: &witx::Id, s: &witx::StructDatatype) -> TokenStream {
     let ident = names.type_(name);
+    let size = s.mem_size_align().size as u32;
+    let align = s.mem_size_align().align as u32;
+
     let member_decls = s.members.iter().map(|m| {
         let name = names.struct_member(&m.name);
         let type_ = names.type_ref(&m.tref);
         quote!(pub #name: #type_)
     });
-    let size = s.mem_size_align().size as u32;
-    let align = s.mem_size_align().align as u32;
+    let member_valids = s.member_layout().into_iter().map(|ml| {
+        let type_ = names.type_ref(&ml.member.tref);
+        let offset = ml.offset as u32;
+        quote!( #type_::validate(&ptr.cast(#offset)?)?; )
+    });
 
     quote! {
         #[repr(C)]
@@ -178,8 +184,9 @@ fn define_copy_struct(names: &Names, name: &witx::Id, s: &witx::StructDatatype)
             fn name() -> String {
                 stringify!(#ident).to_owned()
             }
-            fn validate(_ptr: &::memory::GuestPtr<#ident>) -> Result<(), ::memory::GuestError> {
-                Ok(()) // FIXME
+            fn validate(ptr: &::memory::GuestPtr<#ident>) -> Result<(), ::memory::GuestError> {
+                #(#member_valids)*
+                Ok(())
             }
         }
         impl ::memory::GuestTypeCopy for #ident {}
diff --git a/crates/memory/src/memory.rs b/crates/memory/src/memory.rs
index c24a272d6c..d33f4d707c 100644
--- a/crates/memory/src/memory.rs
+++ b/crates/memory/src/memory.rs
@@ -67,6 +67,15 @@ impl<'a, T: GuestType> GuestPtr<'a, T> {
     pub fn as_raw(&self) -> *const u8 {
         (self.mem.ptr as usize + self.region.start as usize) as *const u8
     }
+
+    pub fn elem(&self, elements: i32) -> Result<GuestPtr<'a, T>, GuestError> {
+        self.mem
+            .ptr(self.region.start + (elements * self.region.len as i32) as u32)
+    }
+
+    pub fn cast<TT: GuestType>(&self, offset: u32) -> Result<GuestPtr<'a, TT>, GuestError> {
+        self.mem.ptr(self.region.start + offset)
+    }
 }
 
 impl<'a, T: GuestTypeCopy> GuestPtr<'a, T> {
diff --git a/test.witx b/test.witx
index af5af5441f..87e11396d7 100644
--- a/test.witx
+++ b/test.witx
@@ -34,7 +34,6 @@
     (param $an_int u32)
     (result $error $errno)
     (result $doubled_it f32))
-
   (@interface func (export "sum_of_pair")
     (param $an_pair $pair_ints)
     (result $error $errno)