diff --git a/rules/string/tgt_refcount.rs b/rules/string/tgt_refcount.rs
index 5e7f50ff0..a7b580240 100644
--- a/rules/string/tgt_refcount.rs
+++ b/rules/string/tgt_refcount.rs
@@ -122,7 +122,8 @@ fn f18(a0: Vec<i8>, a1: Ptr<i8>) -> bool {
 // TODO: This should return a0
 fn f21(a0: &mut Vec<i8>, a1: usize, a2: i8) -> Vec<i8> {
     a0.pop();
-    a0.resize(a0.len() + (a1) as usize, a2);
+    let __len = a0.len() + (a1) as usize;
+    a0.resize(__len, a2);
     a0.push(0);
     a0.clone()
 }
diff --git a/tests/unit/out/refcount/string_repeat_append.rs b/tests/unit/out/refcount/string_repeat_append.rs
new file mode 100644
index 000000000..f19eeb24f
--- /dev/null
+++ b/tests/unit/out/refcount/string_repeat_append.rs
@@ -0,0 +1,175 @@
+extern crate libcc2rs;
+use libcc2rs::*;
+use std::cell::RefCell;
+use std::collections::BTreeMap;
+use std::io::prelude::*;
+use std::io::{Read, Seek, Write};
+use std::os::fd::AsFd;
+use std::rc::{Rc, Weak};
+pub fn append_to_reference_0(s: Ptr<Vec<i8>>) {
+    {
+        s.with_mut(|__v: &mut Vec<i8>| __v.pop());
+        let __len = (*s.upgrade().deref()).len() + (1_usize) as usize;
+        s.with_mut(|__v: &mut Vec<i8>| __v.resize(__len, ('r' as i8)));
+        s.with_mut(|__v: &mut Vec<i8>| __v.push(0));
+        (*s.upgrade().deref()).clone()
+    };
+}
+pub fn main() {
+    __cpp2rust_init_globals();
+    std::process::exit(main_0());
+}
+fn main_0() -> i32 {
+    let lengths: Value<Box<[usize]>> = Rc::new(RefCell::new(Box::new([
+        0_usize, 1_usize, 2_usize, 3_usize, 7_usize, 8_usize, 15_usize, 16_usize, 31_usize,
+        64_usize,
+    ])));
+    let counts: Value<Box<[usize]>> = Rc::new(RefCell::new(Box::new([
+        0_usize, 1_usize, 2_usize, 3_usize, 8_usize, 33_usize,
+    ])));
+    let characters: Value<Box<[i8]>> = Rc::new(RefCell::new(Box::new([
+        0_i8,
+        1_i8,
+        2_i8,
+        7_i8,
+        9_i8,
+        10_i8,
+        13_i8,
+        31_i8,
+        32_i8,
+        42_i8,
+        65_i8,
+        90_i8,
+        97_i8,
+        100_i8,
+        127_i8,
+        (-128_i32 as i8),
+        (-127_i32 as i8),
+        (-64_i32 as i8),
+        (-2_i32 as i8),
+        (-1_i32 as i8),
+    ])));
+    let mut initial: [i8; 5] = [
+        ('a' as i8),
+        0_i8,
+        ('b' as i8),
+        (-128_i32 as i8),
+        (-1_i32 as i8),
+    ];
+    let mut cases: usize = 0_usize;
+    'loop_: for length in IterRange::new(
+        (lengths.as_pointer() as Ptr<usize>),
+        (lengths.as_pointer() as Ptr<usize>).offset((10_i64) as isize),
+    ) {
+        let mut length: usize = (length.read());
+        'loop_: for count in IterRange::new(
+            (counts.as_pointer() as Ptr<usize>),
+            (counts.as_pointer() as Ptr<usize>).offset((6_i64) as isize),
+        ) {
+            let mut count: usize = (count.read());
+            'loop_: for character in IterRange::new(
+                (characters.as_pointer() as Ptr<i8>),
+                (characters.as_pointer() as Ptr<i8>).offset((20_i64) as isize),
+            ) {
+                let character: Value<i8> = Rc::new(RefCell::new((character.read())));
+                let mut shrink: i32 = 0;
+                'loop_: while (shrink < 2) {
+                    let s: Value<Vec<i8>> = Rc::new(RefCell::new(
+                        vec![('x' as i8); (length) as usize]
+                            .iter()
+                            .cloned()
+                            .chain(std::iter::once(0))
+                            .collect(),
+                    ));
+                    let mut i: usize = 0_usize;
+                    'loop_: while (i < length) {
+                        let __rhs = initial[((i)
+                            .wrapping_rem((::std::mem::size_of::<[i8; 5]>() as usize)))
+                            as usize];
+                        (*s.borrow_mut())[i] = __rhs;
+                        i.prefix_inc();
+                    }
+                    if (shrink != 0) {
+                        (*s.borrow_mut()).shrink_to_fit();
+                    }
+                    {
+                        (*s.borrow_mut()).pop();
+                        let __len = (*s.borrow()).len() + (count) as usize;
+                        (*s.borrow_mut()).resize(__len, ({ (*character.borrow()) }));
+                        (*s.borrow_mut()).push(0);
+                        (*s.borrow()).clone()
+                    };
+                    assert!(({ (((*s.borrow()).len() - 1) == (length).wrapping_add(count)) }));
+                    let mut data: Ptr<i8> = s.decay();
+                    let mut i: usize = 0_usize;
+                    'loop_: while (i < (length).wrapping_add(count)) {
+                        assert!(
+                            ({
+                                ({ ((elem!(data, i).read()) as i32) } == {
+                                    ((if (i < length) {
+                                        initial[((i).wrapping_rem(
+                                            (::std::mem::size_of::<[i8; 5]>() as usize),
+                                        )) as usize]
+                                    } else {
+                                        (*character.borrow())
+                                    }) as i32)
+                                })
+                            })
+                        );
+                        i.prefix_inc();
+                    }
+                    assert!(({ (((elem!(data, ((*s.borrow()).len() - 1)).read()) as i32) == 0) }));
+                    cases.prefix_inc();
+                    shrink.prefix_inc();
+                }
+            }
+        }
+    }
+    let mut unboxed: Vec<i8> = {
+        let mut __bytes = Ptr::<i8>::from_string_literal(b"a").to_c_bytes();
+        __bytes.push(0);
+        __bytes
+    };
+    {
+        unboxed.pop();
+        let __len = unboxed.len() + (2_usize) as usize;
+        unboxed.resize(__len, ('b' as i8));
+        unboxed.push(0);
+        unboxed.clone()
+    };
+    assert!(
+        Ptr::<i8>::from_string_literal(b"abb")
+            .with_c_str(|__s| unboxed[..unboxed.len().saturating_sub(1)] == *__s)
+    );
+    let indirect: Value<Vec<i8>> = Rc::new(RefCell::new({
+        let mut __bytes = Ptr::<i8>::from_string_literal(b"c").to_c_bytes();
+        __bytes.push(0);
+        __bytes
+    }));
+    ({ append_to_reference_0(indirect.as_pointer()) });
+    assert!(
+        ({
+            Ptr::<i8>::from_string_literal(b"cr").with_c_str(|__s| {
+                (*indirect.borrow())[..(*indirect.borrow()).len().saturating_sub(1)] == *__s
+            })
+        })
+    );
+    let mut pointer: Ptr<Vec<i8>> = (indirect.as_pointer());
+    {
+        pointer.with_mut(|__v: &mut Vec<i8>| __v.pop());
+        let __len = (*pointer.upgrade().deref()).len() + (0_usize) as usize;
+        pointer.with_mut(|__v: &mut Vec<i8>| __v.resize(__len, ('\0' as i8)));
+        pointer.with_mut(|__v: &mut Vec<i8>| __v.push(0));
+        (*pointer.upgrade().deref()).clone()
+    };
+    assert!(
+        ({
+            Ptr::<i8>::from_string_literal(b"cr").with_c_str(|__s| {
+                (*indirect.borrow())[..(*indirect.borrow()).len().saturating_sub(1)] == *__s
+            })
+        })
+    );
+    println!("checked {} appends", cases);
+    return 0;
+}
+pub fn __cpp2rust_init_globals() {}
diff --git a/tests/unit/out/unsafe/string_repeat_append.rs b/tests/unit/out/unsafe/string_repeat_append.rs
new file mode 100644
index 000000000..5ae7955d8
--- /dev/null
+++ b/tests/unit/out/unsafe/string_repeat_append.rs
@@ -0,0 +1,168 @@
+extern crate libc;
+use libc::*;
+extern crate libcc2rs;
+use libcc2rs::*;
+use std::collections::BTreeMap;
+use std::io::{Read, Seek, Write};
+use std::os::fd::{AsFd, FromRawFd, IntoRawFd};
+use std::rc::Rc;
+pub unsafe fn append_to_reference_0(s: *mut Vec<libc::c_char>) {
+    (*s).splice(
+        (*s).len() - 1..(*s).len() - 1,
+        ::std::vec::from_elem(('r' as libc::c_char), 1_usize as usize),
+    );
+}
+pub fn main() {
+    unsafe {
+        __cpp2rust_init_globals();
+        std::process::exit(main_0() as i32);
+    }
+}
+unsafe fn main_0() -> i32 {
+    let lengths: [usize; 10] = [
+        0_usize, 1_usize, 2_usize, 3_usize, 7_usize, 8_usize, 15_usize, 16_usize, 31_usize,
+        64_usize,
+    ];
+    let counts: [usize; 6] = [0_usize, 1_usize, 2_usize, 3_usize, 8_usize, 33_usize];
+    let characters: [libc::c_char; 20] = [
+        (0 as libc::c_char),
+        (1 as libc::c_char),
+        (2 as libc::c_char),
+        (7 as libc::c_char),
+        (9 as libc::c_char),
+        (10 as libc::c_char),
+        (13 as libc::c_char),
+        (31 as libc::c_char),
+        (32 as libc::c_char),
+        (42 as libc::c_char),
+        (65 as libc::c_char),
+        (90 as libc::c_char),
+        (97 as libc::c_char),
+        (100 as libc::c_char),
+        (127 as libc::c_char),
+        (-128_i32 as libc::c_char),
+        (-127_i32 as libc::c_char),
+        (-64_i32 as libc::c_char),
+        (-2_i32 as libc::c_char),
+        (-1_i32 as libc::c_char),
+    ];
+    let initial: [libc::c_char; 5] = [
+        ('a' as libc::c_char),
+        (0 as libc::c_char),
+        ('b' as libc::c_char),
+        (-128_i32 as libc::c_char),
+        (-1_i32 as libc::c_char),
+    ];
+    let mut cases: usize = 0_usize;
+    'loop_: for length in
+        IterRange::new(lengths.as_ptr(), lengths.as_ptr().offset((10_i64) as isize))
+    {
+        let mut length: usize = (*length);
+        'loop_: for count in
+            IterRange::new(counts.as_ptr(), counts.as_ptr().offset((6_i64) as isize))
+        {
+            let mut count: usize = (*count);
+            'loop_: for character in IterRange::new(
+                characters.as_ptr(),
+                characters.as_ptr().offset((20_i64) as isize),
+            ) {
+                let mut character: libc::c_char = (*character);
+                let mut shrink: i32 = 0;
+                'loop_: while ((shrink) < (2)) {
+                    let mut s: Vec<libc::c_char> = vec![('x' as libc::c_char); (length) as usize]
+                        .iter()
+                        .cloned()
+                        .chain(std::iter::once(0))
+                        .collect();
+                    let mut i: usize = 0_usize;
+                    'loop_: while ((i) < (length)) {
+                        s[(i)] = initial[((i)
+                            .wrapping_rem((::std::mem::size_of::<[libc::c_char; 5]>() as usize)))];
+                        i.prefix_inc();
+                    }
+                    if (shrink != 0) {
+                        s.shrink_to_fit();
+                    }
+                    s.splice(
+                        s.len() - 1..s.len() - 1,
+                        ::std::vec::from_elem(character, count as usize),
+                    );
+                    assert!(((s.len() - 1) == ((length).wrapping_add(count))));
+                    let mut data: *const libc::c_char = (s.as_mut_ptr()).cast_const();
+                    let mut i: usize = 0_usize;
+                    'loop_: while ((i) < ((length).wrapping_add(count))) {
+                        assert!(
+                            (((*data.offset((i) as isize)) as i32)
+                                == ((if ((i) < (length)) {
+                                    initial[((i).wrapping_rem(
+                                        (::std::mem::size_of::<[libc::c_char; 5]>() as usize),
+                                    ))]
+                                } else {
+                                    character
+                                }) as i32))
+                        );
+                        i.prefix_inc();
+                    }
+                    assert!((((*data.offset((s.len() - 1) as isize)) as i32) == (0)));
+                    cases.prefix_inc();
+                    shrink.prefix_inc();
+                }
+            }
+        }
+    }
+    let mut unboxed: Vec<libc::c_char> = std::slice::from_raw_parts(
+        c"a".as_ptr(),
+        (0..).take_while(|&i| *c"a".as_ptr().add(i) != 0).count() + 1,
+    )
+    .to_vec();
+    unboxed.splice(
+        unboxed.len() - 1..unboxed.len() - 1,
+        ::std::vec::from_elem(('b' as libc::c_char), 2_usize as usize),
+    );
+    assert!(
+        unboxed == {
+            std::slice::from_raw_parts(
+                c"abb".as_ptr(),
+                (0..).take_while(|&i| *c"abb".as_ptr().add(i) != 0).count() + 1,
+            )
+            .to_vec()
+        }
+    );
+    let mut indirect: Vec<libc::c_char> = std::slice::from_raw_parts(
+        c"c".as_ptr(),
+        (0..).take_while(|&i| *c"c".as_ptr().add(i) != 0).count() + 1,
+    )
+    .to_vec();
+    (unsafe { append_to_reference_0(&mut indirect) });
+    assert!(
+        indirect == {
+            std::slice::from_raw_parts(
+                c"cr".as_ptr(),
+                (0..).take_while(|&i| *c"cr".as_ptr().add(i) != 0).count() + 1,
+            )
+            .to_vec()
+        }
+    );
+    let mut pointer: *mut Vec<libc::c_char> = (&mut indirect as *mut Vec<libc::c_char>);
+    (*pointer).splice(
+        (*pointer).len() - 1..(*pointer).len() - 1,
+        ::std::vec::from_elem(('\0' as libc::c_char), 0_usize as usize),
+    );
+    assert!(
+        indirect == {
+            std::slice::from_raw_parts(
+                c"cr".as_ptr(),
+                (0..).take_while(|&i| *c"cr".as_ptr().add(i) != 0).count() + 1,
+            )
+            .to_vec()
+        }
+    );
+    (unsafe {
+        libc::printf(
+            c"checked %zu appends\n".as_ptr() as *const libc::c_char,
+            (cases),
+        )
+    });
+    return 0;
+}
+pub unsafe fn __cpp2rust_init_globals() {}
diff --git a/tests/unit/string_repeat_append.cpp b/tests/unit/string_repeat_append.cpp
new file mode 100644
index 000000000..0bf287ecd
--- /dev/null
+++ b/tests/unit/string_repeat_append.cpp
@@ -0,0 +1,47 @@
+#include <cassert>
+#include <cstdio>
+#include <string>
+
+void append_to_reference(std::string &s) { s.append(1, 'r'); }
+
+int main() {
+  const std::size_t lengths[] = {0, 1, 2, 3, 7, 8, 15, 16, 31, 64};
+  const std::size_t counts[] = {0, 1, 2, 3, 8, 33};
+  const char characters[] = {0,  1,  2,  7,   9,   10,   13,   31,  32, 42,
+                             65, 90, 97, 100, 127, -128, -127, -64, -2, -1};
+  const char initial[] = {'a', 0, 'b', -128, -1};
+  std::size_t cases = 0;
+  for (std::size_t length : lengths) {
+    for (std::size_t count : counts) {
+      for (char character : characters) {
+        for (int shrink = 0; shrink < 2; ++shrink) {
+          std::string s(length, 'x');
+          for (std::size_t i = 0; i < length; ++i)
+            s[i] = initial[i % std::size_t(sizeof(initial))];
+          if (shrink)
+            s.shrink_to_fit();
+          s.append(count, character);
+          assert(s.size() == length + count);
+          const char *data = s.data();
+          for (std::size_t i = 0; i < length + count; ++i)
+            assert(data[i] == (i < length
+                                   ? initial[i % std::size_t(sizeof(initial))]
+                                   : character));
+          assert(data[s.size()] == 0);
+          ++cases;
+        }
+      }
+    }
+  }
+  std::string unboxed = "a";
+  unboxed.append(2, 'b');
+  assert(unboxed == "abb");
+  std::string indirect = "c";
+  append_to_reference(indirect);
+  assert(indirect == "cr");
+  std::string *pointer = &indirect;
+  pointer->append(std::size_t(0), '\0');
+  assert(indirect == "cr");
+  printf("checked %zu appends\n", cases);
+  return 0;
+}