diff --git a/src/librustc/middle/trans/base.rs b/src/librustc/middle/trans/base.rs
index f14ea279c2d..5fa0ade6055 100644
--- a/src/librustc/middle/trans/base.rs
+++ b/src/librustc/middle/trans/base.rs
@@ -52,7 +52,7 @@ use middle::trans::foreign;
 use middle::trans::glue;
 use middle::trans::inline;
 use middle::trans::machine;
-use middle::trans::machine::llsize_of;
+use middle::trans::machine::{llalign_of_min, llsize_of};
 use middle::trans::meth;
 use middle::trans::monomorphize;
 use middle::trans::reachable;
@@ -1442,12 +1442,7 @@ pub fn with_cond(bcx: block, val: ValueRef, f: &fn(block) -> block) -> block {
     next_cx
 }
 
-pub fn call_memcpy(cx: block, dst: ValueRef, src: ValueRef,
-                   n_bytes: ValueRef) {
-    // FIXME (Related to #1645, I think?): Provide LLVM with better
-    // alignment information when the alignment is statically known (it must
-    // be nothing more than a constant int, or LLVM complains -- not even a
-    // constant element of a tydesc works).
+pub fn call_memcpy(cx: block, dst: ValueRef, src: ValueRef, n_bytes: ValueRef, align: u32) {
     let _icx = cx.insn_ctxt("call_memcpy");
     let ccx = cx.ccx();
     let key = match ccx.sess.targ_cfg.arch {
@@ -1462,7 +1457,7 @@ pub fn call_memcpy(cx: block, dst: ValueRef, src: ValueRef,
     let src_ptr = PointerCast(cx, src, T_ptr(T_i8()));
     let dst_ptr = PointerCast(cx, dst, T_ptr(T_i8()));
     let size = IntCast(cx, n_bytes, ccx.int_type);
-    let align = C_i32(1i32);
+    let align = C_i32(align as i32);
     let volatile = C_i1(false);
     Call(cx, memcpy, [dst_ptr, src_ptr, size, align, volatile]);
 }
@@ -1471,8 +1466,10 @@ pub fn memcpy_ty(bcx: block, dst: ValueRef, src: ValueRef, t: ty::t) {
     let _icx = bcx.insn_ctxt("memcpy_ty");
     let ccx = bcx.ccx();
     if ty::type_is_structural(t) {
-        let llsz = llsize_of(ccx, type_of::type_of(ccx, t));
-        call_memcpy(bcx, dst, src, llsz);
+        let llty = type_of::type_of(ccx, t);
+        let llsz = llsize_of(ccx, llty);
+        let llalign = llalign_of_min(ccx, llty);
+        call_memcpy(bcx, dst, src, llsz, llalign as u32);
     } else {
         Store(bcx, Load(bcx, src), dst);
     }
diff --git a/src/librustc/middle/trans/closure.rs b/src/librustc/middle/trans/closure.rs
index 57df27ef199..335dd47b78b 100644
--- a/src/librustc/middle/trans/closure.rs
+++ b/src/librustc/middle/trans/closure.rs
@@ -521,7 +521,7 @@ pub fn make_opaque_cbox_take_glue(
             [opaque_tydesc, sz],
             expr::SaveIn(rval));
         let cbox_out = PointerCast(bcx, Load(bcx, rval), llopaquecboxty);
-        call_memcpy(bcx, cbox_out, cbox_in, sz);
+        call_memcpy(bcx, cbox_out, cbox_in, sz, 1);
         Store(bcx, cbox_out, cboxptr);
 
         // Take the (deeply cloned) type descriptor
diff --git a/src/librustc/middle/trans/foreign.rs b/src/librustc/middle/trans/foreign.rs
index 7bfec9c89cb..ff17dd82687 100644
--- a/src/librustc/middle/trans/foreign.rs
+++ b/src/librustc/middle/trans/foreign.rs
@@ -787,7 +787,7 @@ pub fn trans_intrinsic(ccx: @CrateContext,
                 let llsrcptr = PointerCast(bcx, llsrcptr, T_ptr(T_i8()));
 
                 let llsize = llsize_of(ccx, llintype);
-                call_memcpy(bcx, lldestptr, llsrcptr, llsize);
+                call_memcpy(bcx, lldestptr, llsrcptr, llsize, 1);
             }
         }
         ~"needs_drop" => {
diff --git a/src/librustc/middle/trans/tvec.rs b/src/librustc/middle/trans/tvec.rs
index 29e026189db..278a7355892 100644
--- a/src/librustc/middle/trans/tvec.rs
+++ b/src/librustc/middle/trans/tvec.rs
@@ -125,7 +125,7 @@ pub fn duplicate_uniq(bcx: block, vptr: ValueRef, vec_ty: ty::t) -> Result {
 
     let data_ptr = get_dataptr(bcx, get_bodyptr(bcx, vptr));
     let new_data_ptr = get_dataptr(bcx, get_bodyptr(bcx, newptr));
-    base::call_memcpy(bcx, new_data_ptr, data_ptr, fill);
+    base::call_memcpy(bcx, new_data_ptr, data_ptr, fill, 1);
 
     let bcx = if ty::type_needs_drop(bcx.tcx(), unit_ty) {
         iter_vec_raw(bcx, new_data_ptr, vec_ty, fill, glue::take_ty)
@@ -370,7 +370,7 @@ pub fn write_content(bcx: block,
                     let bytes = s.len() + 1; // copy null-terminator too
                     let llbytes = C_uint(bcx.ccx(), bytes);
                     let llcstr = C_cstr(bcx.ccx(), s);
-                    base::call_memcpy(bcx, lldest, llcstr, llbytes);
+                    base::call_memcpy(bcx, lldest, llcstr, llbytes, 1);
                     return bcx;
                 }
             }