diff --git a/examples/repl/cmdline.rs b/examples/repl/cmdline.rs
index 9e59b08b8..09c0225a6 100644
--- a/examples/repl/cmdline.rs
+++ b/examples/repl/cmdline.rs
@@ -1,3 +1,4 @@
+use std::ffi::CString;
 use std::str::FromStr;
 
 use deltachat::chatlist::*;
@@ -568,13 +569,14 @@ pub unsafe fn dc_cmdline(context: &Context, line: &str) -> Result<(), failure::E
             dc_imex(context, 2, context.get_blobdir(), 0 as *const libc::c_char);
         }
         "export-setup" => {
-            let setup_code: *mut libc::c_char = dc_create_setup_code(context);
+            let setup_code = dc_create_setup_code(context);
+            let setup_code_c = CString::new(setup_code.clone()).unwrap();
             let file_name: *mut libc::c_char = dc_mprintf(
                 b"%s/autocrypt-setup-message.html\x00" as *const u8 as *const libc::c_char,
                 context.get_blobdir(),
             );
             let file_content: *mut libc::c_char;
-            file_content = dc_render_setup_file(context, setup_code);
+            file_content = dc_render_setup_file(context, setup_code_c.as_ptr());
             if !file_content.is_null()
                 && 0 != dc_write_file(
                     context,
@@ -586,14 +588,13 @@ pub unsafe fn dc_cmdline(context: &Context, line: &str) -> Result<(), failure::E
                 println!(
                     "Setup message written to: {}\nSetup code: {}",
                     as_str(file_name),
-                    as_str(setup_code),
+                    &setup_code,
                 )
             } else {
                 bail!("");
             }
             free(file_content as *mut libc::c_void);
             free(file_name as *mut libc::c_void);
-            free(setup_code as *mut libc::c_void);
         }
         "poke" => {
             ensure!(0 != poke_spec(context, arg1_c), "Poke failed");
diff --git a/src/dc_imex.rs b/src/dc_imex.rs
index be13b7aa8..f640bf72e 100644
--- a/src/dc_imex.rs
+++ b/src/dc_imex.rs
@@ -105,7 +105,7 @@ pub unsafe fn dc_initiate_key_transfer(context: &Context) -> *mut libc::c_char {
     if 0 == dc_alloc_ongoing(context) {
         return 0 as *mut libc::c_char;
     }
-    setup_code = dc_create_setup_code(context);
+    setup_code = to_cstring(dc_create_setup_code(context));
     if !setup_code.is_null() {
         /* this may require a keypair to be created. this may take a second ... */
         if !context
@@ -282,7 +282,7 @@ pub unsafe extern "C" fn dc_render_setup_file(
     ret_setupfilecontent
 }
 
-pub unsafe fn dc_create_setup_code(_context: &Context) -> *mut libc::c_char {
+pub fn dc_create_setup_code(_context: &Context) -> String {
     let mut random_val: uint16_t;
     let mut rng = thread_rng();
     let mut ret = String::new();
@@ -302,7 +302,7 @@ pub unsafe fn dc_create_setup_code(_context: &Context) -> *mut libc::c_char {
         );
     }
 
-    to_cstring(ret)
+    ret
 }
 
 // TODO should return bool /rtn
diff --git a/tests/stress.rs b/tests/stress.rs
index 89beddf4b..d5518b9e2 100644
--- a/tests/stress.rs
+++ b/tests/stress.rs
@@ -1,6 +1,7 @@
 //! Stress some functions for testing; if used as a lib, this file is obsolete.
 
 use std::collections::HashSet;
+use std::ffi::CString;
 
 use mmime::mailimf_types::*;
 use tempfile::{tempdir, TempDir};
@@ -527,11 +528,11 @@ unsafe fn stress_functions(context: &Context) {
     );
     free(buf_1 as *mut libc::c_void);
     if 0 != dc_is_configured(context) {
-        let setupcode: *mut libc::c_char;
         let setupfile: *mut libc::c_char;
-        setupcode = dc_create_setup_code(context);
-        assert!(!setupcode.is_null());
-        assert_eq!(strlen(setupcode), 44);
+        let setupcode_c =
+            CString::new(dc_create_setup_code(context)).expect("invalid string converted");
+        assert_eq!(setupcode_c.to_bytes().len(), 44);
+        let setupcode = setupcode_c.as_ptr();
         assert!(
             0 != !(*setupcode.offset(4isize) as libc::c_int == '-' as i32
                 && *setupcode.offset(9isize) as libc::c_int == '-' as i32
@@ -596,7 +597,6 @@ unsafe fn stress_functions(context: &Context) {
         );
         free(payload as *mut libc::c_void);
         free(setupfile as *mut libc::c_void);
-        free(setupcode as *mut libc::c_void);
     }
 
     if 0 != dc_is_configured(context) {