diff --git a/src/context.rs b/src/context.rs
index 8c0942944..99d6749d7 100644
--- a/src/context.rs
+++ b/src/context.rs
@@ -249,16 +249,8 @@ unsafe fn cb_set_config(context: &Context, key: *const libc::c_char, value: *con
  *
  * @private @memberof Context
  */
-unsafe fn cb_get_config(
-    context: &Context,
-    key: *const libc::c_char,
-    def: *const libc::c_char,
-) -> *mut libc::c_char {
-    let res = context
-        .sql
-        .get_config(context, as_str(key))
-        .unwrap_or_else(|| to_string(def));
-    to_cstring(res)
+fn cb_get_config(context: &Context, key: &str) -> Option<String> {
+    context.sql.get_config(context, key)
 }
 
 pub unsafe fn dc_context_unref(context: &mut Context) {
diff --git a/src/imap.rs b/src/imap.rs
index b07767372..17b544c49 100644
--- a/src/imap.rs
+++ b/src/imap.rs
@@ -5,7 +5,7 @@ use std::time::{Duration, SystemTime};
 use crate::constants::*;
 use crate::context::Context;
 use crate::dc_loginparam::*;
-use crate::dc_tools::{as_str, to_cstring};
+use crate::dc_tools::to_cstring;
 use crate::oauth2::dc_get_oauth2_access_token;
 use crate::types::*;
 use crate::x::free;
@@ -705,26 +705,16 @@ impl Imap {
 
     fn get_config_last_seen_uid<S: AsRef<str>>(&self, context: &Context, folder: S) -> (u32, u32) {
         let key = format!("imap.mailbox.{}", folder.as_ref());
-        let val1 = unsafe {
-            let key_c = to_cstring(key);
-            let val = (self.get_config)(context, key_c, 0 as *const libc::c_char);
-            free(key_c as *mut _);
-            val
-        };
-        if val1.is_null() {
-            return (0, 0);
+        if let Some(entry) = (self.get_config)(context, &key) {
+            // the entry has the format `imap.mailbox.<folder>=<uidvalidity>:<lastseenuid>`
+            let mut parts = entry.split(':');
+            (
+                parts.next().unwrap().parse().unwrap_or_else(|_| 0),
+                parts.next().unwrap().parse().unwrap_or_else(|_| 0),
+            )
+        } else {
+            (0, 0)
         }
-        let entry = as_str(val1);
-
-        if entry.is_empty() {
-            return (0, 0);
-        }
-        // the entry has the format `imap.mailbox.<folder>=<uidvalidity>:<lastseenuid>`
-        let mut parts = entry.split(':');
-        (
-            parts.next().unwrap().parse().unwrap_or_else(|_| 0),
-            parts.next().unwrap().parse().unwrap_or_else(|_| 0),
-        )
     }
 
     fn fetch_from_single_folder<S: AsRef<str>>(&self, context: &Context, folder: S) -> usize {
diff --git a/src/types.rs b/src/types.rs
index 3cf1043df..47bcbd23c 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -36,8 +36,7 @@ pub type dc_precheck_imf_t =
     unsafe fn(_: &Context, _: *const libc::c_char, _: &str, _: u32) -> libc::c_int;
 pub type dc_set_config_t =
     unsafe fn(_: &Context, _: *const libc::c_char, _: *const libc::c_char) -> ();
-pub type dc_get_config_t =
-    unsafe fn(_: &Context, _: *const libc::c_char, _: *const libc::c_char) -> *mut libc::c_char;
+pub type dc_get_config_t = fn(_: &Context, _: &str) -> Option<String>;
 
 pub type sqlite_int64 = i64;
 pub type sqlite3_int64 = sqlite_int64;