diff --git a/examples/repl/cmdline.rs b/examples/repl/cmdline.rs
index 0e72396d1..204c71de9 100644
--- a/examples/repl/cmdline.rs
+++ b/examples/repl/cmdline.rs
@@ -450,6 +450,7 @@ pub unsafe fn dc_cmdline(context: &Context, line: &str) -> Result<(), failure::E
                  dellocations\n\
                  getlocations [<contact-id>]\n\
                  send <text>\n\
+                 send-garbage\n\
                  sendimage <file> [<text>]\n\
                  sendfile <file>\n\
                  draft [<text>]\n\
@@ -948,6 +949,15 @@ pub unsafe fn dc_cmdline(context: &Context, line: &str) -> Result<(), failure::E
                 bail!("Sending failed.");
             }
         }
+        "send-garbage" => {
+            ensure!(!sel_chat.is_null(), "No chat selected.");
+            let msg = b"\xff\x00"; // NUL-terminated C-string, that is malformed utf-8
+            if 0 != dc_send_text_msg(context, dc_chat_get_id(sel_chat), msg.as_ptr().cast()) {
+                println!("Malformed utf-8 succesfully send. Not nice.");
+            } else {
+                bail!("Garbage sending failed, as expected.");
+            }
+        }
         "sendempty" => {
             ensure!(!sel_chat.is_null(), "No chat selected.");
             if 0 != dc_send_text_msg(
diff --git a/examples/repl/main.rs b/examples/repl/main.rs
index 28f923c3f..7cc700af8 100644
--- a/examples/repl/main.rs
+++ b/examples/repl/main.rs
@@ -3,6 +3,7 @@
 //!
 //! Usage:  cargo run --example repl --release -- <databasefile>
 //! All further options can be set using the set-command (type ? for help).
+#![feature(ptr_cast)]
 
 #[macro_use]
 extern crate deltachat;
@@ -290,7 +291,7 @@ const DB_COMMANDS: [&'static str; 11] = [
     "housekeeping",
 ];
 
-const CHAT_COMMANDS: [&'static str; 24] = [
+const CHAT_COMMANDS: [&'static str; 25] = [
     "listchats",
     "listarchived",
     "chat",
@@ -308,6 +309,7 @@ const CHAT_COMMANDS: [&'static str; 24] = [
     "dellocations",
     "getlocations",
     "send",
+    "send-garbage",
     "sendimage",
     "sendfile",
     "draft",
diff --git a/src/dc_chat.rs b/src/dc_chat.rs
index 6a819e8a5..0b4307484 100644
--- a/src/dc_chat.rs
+++ b/src/dc_chat.rs
@@ -976,6 +976,11 @@ pub unsafe fn dc_send_text_msg(
         return 0;
     }
 
+    if let Err(err) = as_str_safe(text_to_send) {
+        warn!(context, 0, "{}", err);
+        return 0;
+    }
+
     let mut msg = dc_msg_new(context, 10);
     (*msg).text = dc_strdup(text_to_send);
     let ret = dc_send_msg(context, chat_id, msg);
diff --git a/src/dc_tools.rs b/src/dc_tools.rs
index d39317c7b..11fc46717 100644
--- a/src/dc_tools.rs
+++ b/src/dc_tools.rs
@@ -4,6 +4,7 @@ use std::fs;
 use std::time::SystemTime;
 
 use chrono::{Local, TimeZone};
+use failure::format_err;
 use mmime::mailimf_types::*;
 use rand::{thread_rng, Rng};
 
@@ -1563,13 +1564,16 @@ pub fn to_string_lossy(s: *const libc::c_char) -> String {
 }
 
 pub fn as_str<'a>(s: *const libc::c_char) -> &'a str {
+    as_str_safe(s).unwrap_or_else(|err| panic!("{}", err))
+}
+
+pub fn as_str_safe<'a>(s: *const libc::c_char) -> Result<&'a str, failure::Error> {
     assert!(!s.is_null(), "cannot be used on null pointers");
 
     let cstr = unsafe { CStr::from_ptr(s) };
 
-    cstr.to_str().unwrap_or_else(|err| {
-        panic!("Non utf8 string: '{:?}' ({:?})", cstr.to_bytes(), err);
-    })
+    cstr.to_str()
+        .map_err(|err| format_err!("Non utf8 string: '{:?}' ({:?})", cstr.to_bytes(), err))
 }
 
 /// Convert a C `*char` pointer to a [std::path::Path] slice.