diff --git a/compiler/rustc_codegen_ssa/src/mir/statement.rs b/compiler/rustc_codegen_ssa/src/mir/statement.rs
index afbef86bd089e..950a4112ebfae 100644
--- a/compiler/rustc_codegen_ssa/src/mir/statement.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/statement.rs
@@ -86,7 +86,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     .layout_of(bx.typing_env().as_query_input(pointee))
                     .expect("expected pointee to have a layout");
                 let elem_size = pointee_layout.layout.size().bytes();
-                let bytes = bx.mul(count, bx.const_usize(elem_size));
+                let bytes = bx.unchecked_sumul(count, bx.const_usize(elem_size));
 
                 let align = pointee_layout.layout.align.abi;
                 let dst = dst_val.immediate();
diff --git a/tests/codegen-llvm/intrinsics/copy_nonoverlapping.rs b/tests/codegen-llvm/intrinsics/copy_nonoverlapping.rs
new file mode 100644
index 0000000000000..84a1f713ce68c
--- /dev/null
+++ b/tests/codegen-llvm/intrinsics/copy_nonoverlapping.rs
@@ -0,0 +1,17 @@
+//@ compile-flags: -Copt-level=3 -C no-prepopulate-passes
+//@ only-64bit (so I don't need to worry about usize)
+
+#![crate_type = "lib"]
+#![feature(core_intrinsics)]
+
+// This deals in a count of elements, not bytes, so we need to multiply.
+// Ensure we preserve UB from a count too high to be valid.
+use std::intrinsics::copy_nonoverlapping;
+
+// CHECK-LABEL: @copy_u16(
+#[no_mangle]
+pub unsafe fn copy_u16(src: *const u16, dst: *mut u16, count: usize) {
+    // CHECK: [[BYTES:%.+]] = mul nuw nsw i64 %count, 2
+    // CHECK: call void @llvm.memcpy.p0.p0.i64(ptr align 2 %dst, ptr align 2 %src, i64 [[BYTES]], i1 false)
+    copy_nonoverlapping(src, dst, count)
+}