diff --git a/src/lib/raft/raft.c b/src/lib/raft/raft.c
index 9b8d69b7..f3fad327 100644
--- a/src/lib/raft/raft.c
+++ b/src/lib/raft/raft.c
@@ -15,6 +15,11 @@ int raft_init(raft_state_t *s, const raft_config_t *cfg)
     /* Validate required callbacks and n_peers before touching *s */
     if (cfg->n_peers < 1)
         return -EINVAL;
+    /* Even cluster sizes (>1) have no fault-tolerance advantage over the next
+     * smaller odd size and can mislead operators into thinking split-brain is
+     * impossible.  Reject to prevent misconfiguration. */
+    if (cfg->n_peers > 1 && cfg->n_peers % 2 == 0)
+        return -EINVAL;
     if (!cfg->cbs)
         return -EINVAL;
     if (!cfg->cbs->on_send_vote_request)
diff --git a/src/lib/testsuite/test_raft.c b/src/lib/testsuite/test_raft.c
index ab6bf4f9..e29f78d6 100644
--- a/src/lib/testsuite/test_raft.c
+++ b/src/lib/testsuite/test_raft.c
@@ -258,7 +258,7 @@ static void test_raft_init_null_become_leader_returns_einval(void)
     cbs.on_become_leader = NULL;
 
     memset(&cfg, 0, sizeof(cfg));
-    cfg.n_peers = 2; cfg.self_idx = 0; cfg.cbs = &cbs;
+    cfg.n_peers = 3; cfg.self_idx = 0; cfg.cbs = &cbs;
 
     TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));
 }
@@ -273,7 +273,7 @@ static void test_raft_init_null_become_follower_returns_einval(void)
     cbs.on_become_follower = NULL;
 
     memset(&cfg, 0, sizeof(cfg));
-    cfg.n_peers = 2; cfg.self_idx = 0; cfg.cbs = &cbs;
+    cfg.n_peers = 3; cfg.self_idx = 0; cfg.cbs = &cbs;
 
     TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));
 }
@@ -288,7 +288,7 @@ static void test_raft_init_null_persist_returns_einval(void)
     cbs.on_persist = NULL;
 
     memset(&cfg, 0, sizeof(cfg));
-    cfg.n_peers = 2; cfg.self_idx = 0; cfg.cbs = &cbs;
+    cfg.n_peers = 3; cfg.self_idx = 0; cfg.cbs = &cbs;
 
     TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));
 }
@@ -303,7 +303,7 @@ static void test_raft_init_null_schedule_timeout_returns_einval(void)
     cbs.on_schedule_timeout = NULL;
 
     memset(&cfg, 0, sizeof(cfg));
-    cfg.n_peers = 2; cfg.self_idx = 0; cfg.cbs = &cbs;
+    cfg.n_peers = 3; cfg.self_idx = 0; cfg.cbs = &cbs;
 
     TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));
 }
@@ -318,7 +318,7 @@ static void test_raft_init_null_cancel_timeout_returns_einval(void)
     cbs.on_cancel_timeout = NULL;
 
     memset(&cfg, 0, sizeof(cfg));
-    cfg.n_peers = 2; cfg.self_idx = 0; cfg.cbs = &cbs;
+    cfg.n_peers = 3; cfg.self_idx = 0; cfg.cbs = &cbs;
 
     TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));
 }
@@ -333,11 +333,47 @@ static void test_raft_init_null_start_election_after_delay_returns_einval(void)
     cbs.on_start_election_after_delay = NULL;
 
     memset(&cfg, 0, sizeof(cfg));
-    cfg.n_peers = 2; cfg.self_idx = 0; cfg.cbs = &cbs;
+    cfg.n_peers = 3; cfg.self_idx = 0; cfg.cbs = &cbs;
 
     TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));
 }
 
+/* n_peers even (>1) → -EINVAL: even-sized clusters have no fault-tolerance
+ * advantage over the next-smaller odd cluster; reject to prevent misconfiguration. */
+static void test_raft_init_even_peers_returns_einval(void)
+{
+    raft_state_t     s;
+    raft_callbacks_t cbs = make_full_cbs();
+    raft_config_t    cfg;
+
+    memset(&s, 0xAB, sizeof(s));
+
+    /* n_peers=2: even, >1 → must fail */
+    memset(&cfg, 0, sizeof(cfg));
+    cfg.n_peers  = 2;
+    cfg.self_idx = 0;
+    cfg.cbs      = &cbs;
+    TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));
+
+    /* n_peers=4: even, >1 → must fail */
+    cfg.n_peers = 4;
+    TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));
+
+    /* n_peers=1: single-node is always valid (odd by convention) */
+    cfg.n_peers = 1;
+    TEST_ASSERT_EQUAL_INT(0, raft_init(&s, &cfg));
+
+    /* n_peers=3: odd, >1 → must succeed */
+    memset(&cfg, 0, sizeof(cfg));
+    cfg.n_peers  = 3;
+    cfg.self_idx = 0;
+    cfg.cbs      = &cbs;
+    TEST_ASSERT_EQUAL_INT(0, raft_init(&s, &cfg));
+
+    /* s must NOT be unchanged after valid inits above */
+    TEST_ASSERT_EQUAL_INT(RAFT_FOLLOWER, s.role);
+}
+
 /* n_peers == 0 → -EINVAL */
 static void test_raft_init_zero_peers_returns_einval(void)
 {
@@ -2849,6 +2885,7 @@ void test_raft(void)
     RUN_TEST(test_raft_init_null_schedule_timeout_returns_einval);
     RUN_TEST(test_raft_init_null_cancel_timeout_returns_einval);
     RUN_TEST(test_raft_init_null_start_election_after_delay_returns_einval);
+    RUN_TEST(test_raft_init_even_peers_returns_einval);
     RUN_TEST(test_raft_init_zero_peers_returns_einval);
     RUN_TEST(test_raft_init_success_fields);
     RUN_TEST(test_raft_init_default_election_timeout);