diff --git a/src/dc_configure.rs b/src/dc_configure.rs
index a50d4db35..8884104f9 100644
--- a/src/dc_configure.rs
+++ b/src/dc_configure.rs
@@ -570,13 +570,13 @@ pub unsafe fn dc_job_do_DC_JOB_CONFIGURE_IMAP(context: &Context, _job: *mut dc_j
                                             {
                                                 param.send_pw = param.mail_pw.clone()
                                             }
-                                            if 0 == dc_exactly_one_bit_set(
+                                            if !dc_exactly_one_bit_set(
                                                 param.server_flags & (0x2 | 0x4),
                                             ) {
                                                 param.server_flags &= !(0x2 | 0x4);
                                                 param.server_flags |= 0x4
                                             }
-                                            if 0 == dc_exactly_one_bit_set(
+                                            if !dc_exactly_one_bit_set(
                                                 param.server_flags & (0x100 | 0x200 | 0x400),
                                             ) {
                                                 param.server_flags &= !(0x100 | 0x200 | 0x400);
@@ -586,7 +586,7 @@ pub unsafe fn dc_job_do_DC_JOB_CONFIGURE_IMAP(context: &Context, _job: *mut dc_j
                                                     0x200
                                                 }
                                             }
-                                            if 0 == dc_exactly_one_bit_set(
+                                            if !dc_exactly_one_bit_set(
                                                 param.server_flags & (0x10000 | 0x20000 | 0x40000),
                                             ) {
                                                 param.server_flags &=
diff --git a/src/dc_tools.rs b/src/dc_tools.rs
index dda2b2584..ec272932c 100644
--- a/src/dc_tools.rs
+++ b/src/dc_tools.rs
@@ -20,8 +20,8 @@ no references to Context and other "larger" classes here. */
 // for carray etc.
 /* ** library-private **********************************************************/
 /* math tools */
-pub unsafe fn dc_exactly_one_bit_set(v: libc::c_int) -> libc::c_int {
-    return (0 != v && 0 == v & v - 1i32) as libc::c_int;
+pub fn dc_exactly_one_bit_set(v: libc::c_int) -> bool {
+    0 != v && 0 == v & v - 1i32
 }
 
 /* string tools */