diff --git a/src/librustc_trans/mir/constant.rs b/src/librustc_trans/mir/constant.rs
index d836d796c41..aa640d3da3c 100644
--- a/src/librustc_trans/mir/constant.rs
+++ b/src/librustc_trans/mir/constant.rs
@@ -811,7 +811,10 @@ impl<'a, 'tcx> MirConstContext<'a, 'tcx> {
                                     consts::ptrcast(llval, ll_t_out)
                                 }
                                 (CastTy::Int(_), CastTy::Ptr(_)) => {
-                                    llvm::LLVMConstIntToPtr(llval, ll_t_out.to_ref())
+                                    let s = signed as llvm::Bool;
+                                    let usize_llval = llvm::LLVMConstIntCast(llval,
+                                        self.ccx.isize_ty().to_ref(), s);
+                                    llvm::LLVMConstIntToPtr(usize_llval, ll_t_out.to_ref())
                                 }
                                 (CastTy::Ptr(_), CastTy::Int(_)) |
                                 (CastTy::FnPtr, CastTy::Int(_)) => {
diff --git a/src/librustc_trans/mir/rvalue.rs b/src/librustc_trans/mir/rvalue.rs
index 9d705eda9fb..65f1129890d 100644
--- a/src/librustc_trans/mir/rvalue.rs
+++ b/src/librustc_trans/mir/rvalue.rs
@@ -313,8 +313,10 @@ impl<'a, 'tcx> MirContext<'a, 'tcx> {
                             (CastTy::Ptr(_), CastTy::Int(_)) |
                             (CastTy::FnPtr, CastTy::Int(_)) =>
                                 bcx.ptrtoint(llval, ll_t_out),
-                            (CastTy::Int(_), CastTy::Ptr(_)) =>
-                                bcx.inttoptr(llval, ll_t_out),
+                            (CastTy::Int(_), CastTy::Ptr(_)) => {
+                                let usize_llval = bcx.intcast(llval, bcx.ccx.isize_ty(), signed);
+                                bcx.inttoptr(usize_llval, ll_t_out)
+                            }
                             (CastTy::Int(_), CastTy::Float) =>
                                 cast_int_to_float(&bcx, signed, llval, ll_t_in, ll_t_out),
                             (CastTy::Float, CastTy::Int(IntTy::I)) =>
diff --git a/src/test/run-pass/issue-43291.rs b/src/test/run-pass/issue-43291.rs
new file mode 100644
index 00000000000..98de8f78859
--- /dev/null
+++ b/src/test/run-pass/issue-43291.rs
@@ -0,0 +1,18 @@
+// Copyright 2018 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.
+
+pub fn main() {
+    assert_eq!(!0usize as *const (), foo(0, 1));
+    assert_eq!(!0usize as *const (), (0i8 - 1) as *const ());
+}
+
+pub fn foo(a: i8, b: i8) -> *const () {
+    (a - b) as *const ()
+}