diff --git a/mbedtls/src/rng/mod.rs b/mbedtls/src/rng/mod.rs
index 770d1a887..5e40e958f 100644
--- a/mbedtls/src/rng/mod.rs
+++ b/mbedtls/src/rng/mod.rs
@@ -27,8 +27,8 @@ use crate::error::{Result, IntoResult};
 use mbedtls_sys::types::raw_types::{c_int, c_uchar};
 use mbedtls_sys::types::size_t;
 
-callback!(EntropyCallbackMut,EntropyCallback:Sync(data: *mut c_uchar, len: size_t) -> c_int);
-callback!(RngCallbackMut,RngCallback:Sync(data: *mut c_uchar, len: size_t) -> c_int);
+callback!(EntropyCallbackMut,EntropyCallback(data: *mut c_uchar, len: size_t) -> c_int);
+callback!(RngCallbackMut,RngCallback(data: *mut c_uchar, len: size_t) -> c_int);
 
 pub trait Random: RngCallback {
     fn random(&mut self, data: &mut [u8]) -> Result<()> where Self: Sized {
diff --git a/mbedtls/src/rng/os_entropy.rs b/mbedtls/src/rng/os_entropy.rs
index 5c72a067b..98eccf506 100644
--- a/mbedtls/src/rng/os_entropy.rs
+++ b/mbedtls/src/rng/os_entropy.rs
@@ -21,7 +21,7 @@ define!(
     #[c_ty(entropy_context)]
     #[repr(C)]
     struct OsEntropy {
-        sources: Vec<Arc<dyn EntropySourceCallback + Send + Sync + 'static>>,
+        sources: Vec<Arc<dyn EntropySourceCallback + 'static>>,
     };
     pub const new: fn() -> Self = entropy_init { sources: Vec::with_capacity(1), };
     const drop: fn(&mut Self) = entropy_free;
@@ -41,7 +41,7 @@ unsafe impl Sync for OsEntropy {}
 
 #[allow(dead_code)]
 impl OsEntropy {
-    pub fn add_source<F: EntropySourceCallback + Send + Sync + 'static>(
+    pub fn add_source<F: EntropySourceCallback + 'static>(
         &mut self,
         source: Arc<F>,
         threshold: size_t,
diff --git a/mbedtls/src/wrapper_macros.rs b/mbedtls/src/wrapper_macros.rs
index 832f625d8..b0c027a4d 100644
--- a/mbedtls/src/wrapper_macros.rs
+++ b/mbedtls/src/wrapper_macros.rs
@@ -15,7 +15,7 @@ macro_rules! as_item {
 macro_rules! callback {
     //{ ($($arg:ident: $ty:ty),*) -> $ret:ty } => {
     //};
-    { $n:ident, $m:ident$( : $sync:ident )*($($arg:ident: $ty:ty),*) -> $ret:ty } => {
+    { $n:ident, $m:ident($($arg:ident: $ty:ty),*) -> $ret:ty } => {
         #[cfg(not(feature="threading"))]
         pub trait $n {
             unsafe extern "C" fn call_mut(user_data: *mut ::mbedtls_sys::types::raw_types::c_void, $($arg:$ty),*) -> $ret where Self: Sized;
@@ -24,7 +24,7 @@ macro_rules! callback {
         }
 
         #[cfg(feature="threading")]
-        pub trait $n $( : $sync )* {
+        pub trait $n {
             unsafe extern "C" fn call_mut(user_data: *mut ::mbedtls_sys::types::raw_types::c_void, $($arg:$ty),*) -> $ret where Self: Sized;
 
             fn data_ptr_mut(&mut self) -> *mut ::mbedtls_sys::types::raw_types::c_void;
@@ -60,7 +60,7 @@ macro_rules! callback {
         }
 
         #[cfg(feature="threading")]
-        pub trait $m $( : $sync )* {
+        pub trait $m {
             unsafe extern "C" fn call(user_data: *mut ::mbedtls_sys::types::raw_types::c_void, $($arg:$ty),*) -> $ret where Self: Sized;
             
             fn data_ptr(&self) -> *mut ::mbedtls_sys::types::raw_types::c_void;
@@ -89,14 +89,14 @@ macro_rules! callback {
         }
     };
     ($t:ident: $($bound:tt)*) => {
-        #[cfg(feature = "threading")]
-        pub trait $t: $($bound)* {}
         #[cfg(not(feature = "threading"))]
+        pub trait $t: $($bound)* {}
+        #[cfg(feature = "threading")]
         pub trait $t: $($bound)* + Sync {}
 
-        #[cfg(feature = "threading")]
-        impl<F: $($bound)*> $t for F {}
         #[cfg(not(feature = "threading"))]
+        impl<F: $($bound)*> $t for F {}
+        #[cfg(feature = "threading")]
         impl<F: $($bound)* + Sync> $t for F {}
     };
 }