fix build

primitives/phragmen/src/reduce.rs

@@ -400,6 +400,7 @@ fn reduce_all<A: IdentifierT>(assignments: &mut Vec<StakedAssignment<A>>) -> u32
 				let common_count = trailing_common(&voter_root_path, &target_root_path);
 
 				// because roots are the same.
+				#[cfg(feature = "std")]
 				debug_assert_eq!(
 					target_root_path.last().unwrap(),
 					voter_root_path.last().unwrap()
@@ -421,7 +422,9 @@ fn reduce_all<A: IdentifierT>(assignments: &mut Vec<StakedAssignment<A>>) -> u32
 							.cloned(),
 					)
 					.collect::<Vec<NodeRef<A>>>();
+
 				// a cycle's length shall always be multiple of two.
+				#[cfg(feature = "std")]
 				debug_assert_eq!(cycle.len() % 2, 0);
 
 				// find minimum of cycle.