diff --git a/src/context.rs b/src/context.rs
index 99d6749d7..29d8525a4 100644
--- a/src/context.rs
+++ b/src/context.rs
@@ -233,13 +233,8 @@ unsafe fn cb_precheck_imf(
     return rfc724_mid_exists;
 }
 
-unsafe fn cb_set_config(context: &Context, key: *const libc::c_char, value: *const libc::c_char) {
-    let v = if value.is_null() {
-        None
-    } else {
-        Some(as_str(value))
-    };
-    context.sql.set_config(context, as_str(key), v).ok();
+fn cb_set_config(context: &Context, key: &str, value: Option<&str>) {
+    context.sql.set_config(context, key, value).ok();
 }
 
 /* *
diff --git a/src/imap.rs b/src/imap.rs
index 17b544c49..3d6336299 100644
--- a/src/imap.rs
+++ b/src/imap.rs
@@ -914,13 +914,7 @@ impl Imap {
         let key = format!("imap.mailbox.{}", folder.as_ref());
         let val = format!("{}:{}", uidvalidity, lastseenuid);
 
-        unsafe {
-            let key_c = to_cstring(key);
-            let val_c = to_cstring(val);
-            (self.set_config)(context, key_c, val_c);
-            free(key_c as *mut _);
-            free(val_c as *mut _);
-        };
+        (self.set_config)(context, &key, Some(&val));
     }
 
     fn fetch_single_msg<S: AsRef<str>>(
diff --git a/src/types.rs b/src/types.rs
index 47bcbd23c..f3d360333 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -34,8 +34,7 @@ the online state. */
 
 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_set_config_t = fn(_: &Context, _: &str, _: Option<&str>) -> ();
 pub type dc_get_config_t = fn(_: &Context, _: &str) -> Option<String>;
 
 pub type sqlite_int64 = i64;