diff --git a/src/comp/middle/trans_ivec.rs b/src/comp/middle/trans_ivec.rs
index d5b82c66436..b2189a92637 100644
--- a/src/comp/middle/trans_ivec.rs
+++ b/src/comp/middle/trans_ivec.rs
@@ -354,11 +354,6 @@ fn trans_append(cx: &@block_ctxt, t: ty::t, orig_lhs: ValueRef,
 
     let unit_ty = ty::sequence_element_type(bcx_tcx(cx), t);
     let llunitty = type_of_or_i8(cx, unit_ty);
-    alt ty::struct(bcx_tcx(cx), t) {
-      ty::ty_istr. { }
-      ty::ty_vec(_) { }
-      _ { bcx_tcx(cx).sess.bug("non-istr/ivec in trans_append"); }
-    }
 
     let rs = size_of(cx, unit_ty);
     let bcx = rs.bcx;
@@ -381,10 +376,31 @@ fn trans_append(cx: &@block_ctxt, t: ty::t, orig_lhs: ValueRef,
     let rhs_len = rhs_len_and_data.len;
     let rhs_data = rhs_len_and_data.data;
     bcx = rhs_len_and_data.bcx;
-    rs = reserve_space(bcx, llunitty, lhs, rhs_len);
-    let lhs_data = rs.val;
+
+    let have_istrs = alt ty::struct(bcx_tcx(cx), t) {
+      ty::ty_istr. { true }
+      ty::ty_vec(_) { false }
+      _ { bcx_tcx(cx).sess.bug("non-istr/ivec in trans_append"); }
+    };
+
+    let extra_len = if have_istrs {
+        // Only need one of the nulls
+        bcx.build.Sub(rhs_len, C_uint(1u))
+    } else { rhs_len };
+
+    rs = reserve_space(bcx, llunitty, lhs, extra_len);
     bcx = rs.bcx;
 
+    let lhs_data = if have_istrs {
+        let lhs_data = rs.val;
+        let lhs_data_without_null_ptr = alloca(bcx, T_ptr(llunitty));
+        incr_ptr(bcx, lhs_data, C_int(-1),
+                 lhs_data_without_null_ptr);
+        bcx.build.Load(lhs_data_without_null_ptr)
+    } else {
+        rs.val
+    };
+
     // If rhs is lhs then our rhs pointer may have changed
     rhs_len_and_data = get_len_and_data(bcx, rhs, unit_ty);
     rhs_data = rhs_len_and_data.data;
diff --git a/src/test/run-pass/istr.rs b/src/test/run-pass/istr.rs
index 6930808f647..8b0eb0ddc05 100644
--- a/src/test/run-pass/istr.rs
+++ b/src/test/run-pass/istr.rs
@@ -39,6 +39,24 @@ fn test_heap_add() {
     assert ~"this should" + ~" totally work" == ~"this should totally work";
 }
 
+fn test_append() {
+    let s = ~"";
+    s += ~"a";
+    assert s == ~"a";
+
+    let s = ~"a";
+    s += ~"b";
+    log s;
+    assert s == ~"ab";
+
+    let s = ~"c";
+    s += ~"offee";
+    assert s == ~"coffee";
+
+    s += ~"&tea";
+    assert s == ~"coffee&tea";
+}
+
 fn main() {
     test_stack_assign();
     test_heap_lit();
@@ -47,4 +65,5 @@ fn main() {
     test_stack_add();
     test_stack_heap_add();
     test_heap_add();
+    test_append();
 }
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