diff --git a/src/librustc_trans/trans/foreign.rs b/src/librustc_trans/trans/foreign.rs
index fb61bab6ade2..abb961d87de9 100644
--- a/src/librustc_trans/trans/foreign.rs
+++ b/src/librustc_trans/trans/foreign.rs
@@ -36,6 +36,7 @@ use syntax::parse::token::{InternedString, special_idents};
 use syntax::parse::token;
 use syntax::{ast};
 use syntax::{attr, ast_map};
+use syntax::print::pprust;
 use util::ppaux::Repr;
 
 ///////////////////////////////////////////////////////////////////////////
@@ -426,16 +427,47 @@ pub fn trans_native_call<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
     return bcx;
 }
 
+// feature gate SIMD types in FFI, since I (huonw) am not sure the
+// ABIs are handled at all correctly.
+fn gate_simd_ffi(tcx: &ty::ctxt, decl: &ast::FnDecl, ty: &ty::BareFnTy) {
+    if !tcx.sess.features.borrow().simd_ffi {
+        let check = |&: ast_ty: &ast::Ty, ty: ty::Ty| {
+            if ty::type_is_simd(tcx, ty) {
+                tcx.sess.span_err(ast_ty.span,
+                              &format!("use of SIMD type `{}` in FFI is highly experimental and \
+                                        may result in invalid code",
+                                       pprust::ty_to_string(ast_ty))[]);
+                tcx.sess.span_help(ast_ty.span,
+                                   "add #![feature(simd_ffi)] to the crate attributes to enable");
+            }
+        };
+        let sig = &ty.sig.0;
+        for (input, ty) in decl.inputs.iter().zip(sig.inputs.iter()) {
+            check(&*input.ty, *ty)
+        }
+        match decl.output {
+            ast::NoReturn(_) => {}
+            ast::Return(ref ty) => check(&**ty, sig.output.unwrap())
+        }
+    }
+}
+
 pub fn trans_foreign_mod(ccx: &CrateContext, foreign_mod: &ast::ForeignMod) {
     let _icx = push_ctxt("foreign::trans_foreign_mod");
     for foreign_item in foreign_mod.items.iter() {
         let lname = link_name(&**foreign_item);
 
-        if let ast::ForeignItemFn(..) = foreign_item.node {
+        if let ast::ForeignItemFn(ref decl, _) = foreign_item.node {
             match foreign_mod.abi {
                 Rust | RustIntrinsic => {}
                 abi => {
                     let ty = ty::node_id_to_type(ccx.tcx(), foreign_item.id);
+                    match ty.sty {
+                        ty::ty_bare_fn(_, bft) => gate_simd_ffi(ccx.tcx(), &**decl, bft),
+                        _ => ccx.tcx().sess.span_bug(foreign_item.span,
+                                                     "foreign fn's sty isn't a bare_fn_ty?")
+                    }
+
                     register_foreign_item_fn(ccx, abi, ty,
                                              &lname.get()[]);
                     // Unlike for other items, we shouldn't call
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 8929bbe0232e..9231d4ad6594 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -72,6 +72,7 @@ static KNOWN_FEATURES: &'static [(&'static str, Status)] = &[
     ("slicing_syntax", Active),
     ("box_syntax", Active),
     ("on_unimplemented", Active),
+    ("simd_ffi", Active),
 
     ("if_let", Accepted),
     ("while_let", Accepted),
@@ -128,6 +129,7 @@ pub struct Features {
     pub visible_private_types: bool,
     pub quote: bool,
     pub old_orphan_check: bool,
+    pub simd_ffi: bool,
 }
 
 impl Features {
@@ -139,6 +141,7 @@ impl Features {
             visible_private_types: false,
             quote: false,
             old_orphan_check: false,
+            simd_ffi: false,
         }
     }
 }
@@ -524,6 +527,7 @@ fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::C
         visible_private_types: cx.has_feature("visible_private_types"),
         quote: cx.has_feature("quote"),
         old_orphan_check: cx.has_feature("old_orphan_check"),
+        simd_ffi: cx.has_feature("simd_ffi"),
     },
     unknown_features)
 }
diff --git a/src/test/compile-fail/feature-gate-simd-ffi.rs b/src/test/compile-fail/feature-gate-simd-ffi.rs
new file mode 100644
index 000000000000..409c85b71980
--- /dev/null
+++ b/src/test/compile-fail/feature-gate-simd-ffi.rs
@@ -0,0 +1,26 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(simd)]
+#![allow(dead_code)]
+
+use std::simd::f32x4;
+
+#[simd] #[derive(Copy)] #[repr(C)] struct LocalSimd(u8, u8);
+
+extern {
+    fn foo() -> f32x4; //~ ERROR use of SIMD type
+    fn bar(x: f32x4); //~ ERROR use of SIMD type
+
+    fn baz() -> LocalSimd; //~ ERROR use of SIMD type
+    fn qux(x: LocalSimd); //~ ERROR use of SIMD type
+}
+
+fn main() {}
diff --git a/src/test/run-make/simd-ffi/simd.rs b/src/test/run-make/simd-ffi/simd.rs
index d5945db94791..76079ddb8bd9 100755
--- a/src/test/run-make/simd-ffi/simd.rs
+++ b/src/test/run-make/simd-ffi/simd.rs
@@ -14,7 +14,7 @@
 // cross-compiled standard libraries.
 #![no_std]
 
-#![feature(simd, link_llvm_intrinsics, lang_items)]
+#![feature(simd, simd_ffi, link_llvm_intrinsics, lang_items)]
 
 
 #[repr(C)]