diff --git a/src/librustc_codegen_llvm/llvm/diagnostic.rs b/src/librustc_codegen_llvm/llvm/diagnostic.rs
index 2c285132226..7f2a9d6984a 100644
--- a/src/librustc_codegen_llvm/llvm/diagnostic.rs
+++ b/src/librustc_codegen_llvm/llvm/diagnostic.rs
@@ -73,9 +73,9 @@ impl OptimizationDiagnostic<'ll> {
                                                                 &mut column,
                                                                 filename,
                                                                 message)
-                )
-            )
-        );
+                ).ok()
+            ).ok()
+        ).ok();
 
         let mut filename = filename.unwrap_or(String::new());
         if filename.is_empty() {
diff --git a/src/librustc_codegen_llvm/llvm/ffi.rs b/src/librustc_codegen_llvm/llvm/ffi.rs
index a907e9799cd..c2b23246b93 100644
--- a/src/librustc_codegen_llvm/llvm/ffi.rs
+++ b/src/librustc_codegen_llvm/llvm/ffi.rs
@@ -26,7 +26,7 @@ use libc::{c_ulonglong, c_void};
 
 use std::ptr::NonNull;
 
-use super::RustStringRef;
+use super::RustString;
 
 pub type Bool = c_uint;
 
@@ -1402,8 +1402,8 @@ extern "C" {
     pub fn LLVMRustDIBuilderCreateOpDeref() -> i64;
     pub fn LLVMRustDIBuilderCreateOpPlusUconst() -> i64;
 
-    pub fn LLVMRustWriteTypeToString(Type: &Type, s: RustStringRef);
-    pub fn LLVMRustWriteValueToString(value_ref: &Value, s: RustStringRef);
+    pub fn LLVMRustWriteTypeToString(Type: &Type, s: &RustString);
+    pub fn LLVMRustWriteValueToString(value_ref: &Value, s: &RustString);
 
     pub fn LLVMIsAConstantInt(value_ref: &Value) -> Option<&Value>;
     pub fn LLVMIsAConstantFP(value_ref: &Value) -> Option<&Value>;
@@ -1478,32 +1478,32 @@ extern "C" {
 
     pub fn LLVMRustGetSectionName(SI: SectionIteratorRef, data: *mut *const c_char) -> size_t;
 
-    pub fn LLVMRustWriteTwineToString(T: &Twine, s: RustStringRef);
+    pub fn LLVMRustWriteTwineToString(T: &Twine, s: &RustString);
 
     pub fn LLVMContextSetDiagnosticHandler(C: &Context,
                                            Handler: DiagnosticHandler,
                                            DiagnosticContext: *mut c_void);
 
     pub fn LLVMRustUnpackOptimizationDiagnostic(DI: &'a DiagnosticInfo,
-                                                pass_name_out: RustStringRef,
-                                                function_out: *mut Option<&'a Value>,
-                                                loc_line_out: *mut c_uint,
-                                                loc_column_out: *mut c_uint,
-                                                loc_filename_out: RustStringRef,
-                                                message_out: RustStringRef);
+                                                pass_name_out: &RustString,
+                                                function_out: &mut Option<&'a Value>,
+                                                loc_line_out: &mut c_uint,
+                                                loc_column_out: &mut c_uint,
+                                                loc_filename_out: &RustString,
+                                                message_out: &RustString);
     pub fn LLVMRustUnpackInlineAsmDiagnostic(DI: &'a DiagnosticInfo,
                                              cookie_out: *mut c_uint,
                                              message_out: *mut Option<&'a Twine>,
                                              instruction_out: *mut Option<&'a Value>);
 
-    pub fn LLVMRustWriteDiagnosticInfoToString(DI: &DiagnosticInfo, s: RustStringRef);
+    pub fn LLVMRustWriteDiagnosticInfoToString(DI: &DiagnosticInfo, s: &RustString);
     pub fn LLVMRustGetDiagInfoKind(DI: &DiagnosticInfo) -> DiagnosticKind;
 
     pub fn LLVMRustSetInlineAsmDiagnosticHandler(C: &Context,
                                                  H: InlineAsmDiagHandler,
                                                  CX: *mut c_void);
 
-    pub fn LLVMRustWriteSMDiagnosticToString(d: &SMDiagnostic, s: RustStringRef);
+    pub fn LLVMRustWriteSMDiagnosticToString(d: &SMDiagnostic, s: &RustString);
 
     pub fn LLVMRustWriteArchive(Dst: *const c_char,
                                 NumMembers: size_t,
diff --git a/src/librustc_codegen_llvm/llvm/mod.rs b/src/librustc_codegen_llvm/llvm/mod.rs
index 20c88d94a41..c27e0d2ae86 100644
--- a/src/librustc_codegen_llvm/llvm/mod.rs
+++ b/src/librustc_codegen_llvm/llvm/mod.rs
@@ -22,6 +22,7 @@ pub use self::CallConv::*;
 pub use self::Linkage::*;
 
 use std::str::FromStr;
+use std::string::FromUtf8Error;
 use std::slice;
 use std::ffi::{CString, CStr};
 use std::cell::RefCell;
@@ -92,20 +93,19 @@ impl FromStr for ArchiveKind {
     }
 }
 
-#[allow(missing_copy_implementations)]
-extern { pub type RustString; }
-type RustStringRef = *mut RustString;
-type RustStringRepr = *mut RefCell<Vec<u8>>;
+#[repr(C)]
+pub struct RustString {
+    bytes: RefCell<Vec<u8>>,
+}
 
 /// Appending to a Rust string -- used by RawRustStringOstream.
 #[no_mangle]
-pub unsafe extern "C" fn LLVMRustStringWriteImpl(sr: RustStringRef,
+pub unsafe extern "C" fn LLVMRustStringWriteImpl(sr: &RustString,
                                                  ptr: *const c_char,
                                                  size: size_t) {
     let slice = slice::from_raw_parts(ptr as *const u8, size as usize);
 
-    let sr = sr as RustStringRepr;
-    (*sr).borrow_mut().extend_from_slice(slice);
+    sr.bytes.borrow_mut().extend_from_slice(slice);
 }
 
 pub fn SetInstructionCallConv(instr: &'a Value, cc: CallConv) {
@@ -229,16 +229,19 @@ pub fn get_param(llfn: &'a Value, index: c_uint) -> &'a Value {
     }
 }
 
-pub fn build_string<F>(f: F) -> Option<String>
-    where F: FnOnce(RustStringRef)
-{
-    let mut buf = RefCell::new(Vec::new());
-    f(&mut buf as RustStringRepr as RustStringRef);
-    String::from_utf8(buf.into_inner()).ok()
+pub fn build_string(f: impl FnOnce(&RustString)) -> Result<String, FromUtf8Error> {
+    let sr = RustString {
+        bytes: RefCell::new(Vec::new()),
+    };
+    f(&sr);
+    String::from_utf8(sr.bytes.into_inner())
 }
 
-pub unsafe fn twine_to_string(tr: &Twine) -> String {
-    build_string(|s| LLVMRustWriteTwineToString(tr, s)).expect("got a non-UTF8 Twine from LLVM")
+pub fn twine_to_string(tr: &Twine) -> String {
+    unsafe {
+        build_string(|s| LLVMRustWriteTwineToString(tr, s))
+            .expect("got a non-UTF8 Twine from LLVM")
+    }
 }
 
 pub fn last_error() -> Option<String> {