diff --git a/substrate/frame/collective/src/lib.rs b/substrate/frame/collective/src/lib.rs
index 00e976bfb9..a6e44b96fe 100644
--- a/substrate/frame/collective/src/lib.rs
+++ b/substrate/frame/collective/src/lib.rs
@@ -211,7 +211,13 @@ decl_storage! {
 	add_extra_genesis {
 		config(phantom): sp_std::marker::PhantomData<I>;
 		config(members): Vec<T::AccountId>;
-		build(|config| Module::<T, I>::initialize_members(&config.members))
+		build(|config| {
+			use sp_std::collections::btree_set::BTreeSet;
+			let members_set: BTreeSet<_> = config.members.iter().collect();
+			assert!(members_set.len() == config.members.len(), "Members cannot contain duplicate accounts.");
+
+			Module::<T, I>::initialize_members(&config.members)
+		});
 	}
 }
 
@@ -1837,4 +1843,13 @@ mod tests {
 			]);
 		})
 	}
+
+	#[test]
+	#[should_panic(expected = "Members cannot contain duplicate accounts.")]
+	fn genesis_build_panics_with_duplicate_members() {
+		collective::GenesisConfig::<Test> {
+			members: vec![1, 2, 3, 1],
+			phantom: Default::default(),
+		}.build_storage().unwrap();
+	}
 }
diff --git a/substrate/frame/membership/src/lib.rs b/substrate/frame/membership/src/lib.rs
index 0d95af4e6f..c834ed2365 100644
--- a/substrate/frame/membership/src/lib.rs
+++ b/substrate/frame/membership/src/lib.rs
@@ -84,6 +84,11 @@ decl_storage! {
 		config(phantom): sp_std::marker::PhantomData<I>;
 		build(|config: &Self| {
 			let mut members = config.members.clone();
+
+			use sp_std::collections::btree_set::BTreeSet;
+			let members_set: BTreeSet<_> = config.members.iter().collect();
+			assert!(members_set.len() == config.members.len(), "Members cannot contain duplicate accounts.");
+
 			members.sort();
 			T::MembershipInitialized::initialize_members(&members);
 			<Members<T, I>>::put(members);
@@ -706,4 +711,13 @@ mod tests {
 			assert_eq!(PRIME.with(|m| *m.borrow()), Membership::prime());
 		});
 	}
+
+	#[test]
+	#[should_panic(expected = "Members cannot contain duplicate accounts.")]
+	fn genesis_build_panics_with_duplicate_members() {
+		pallet_membership::GenesisConfig::<Test> {
+			members: vec![1, 2, 3, 1],
+			phantom: Default::default(),
+		}.build_storage().unwrap();
+	}
 }