diff --git a/src/he/conn.c b/src/he/conn.c
index ea1bc73..347f583 100644
--- a/src/he/conn.c
+++ b/src/he/conn.c
@@ -1223,7 +1223,7 @@ he_return_code_t he_conn_start_pmtu_discovery(he_conn_t *conn) {
 }
 
 uint16_t he_conn_get_effective_pmtu(he_conn_t *conn) {
-  if(!conn || conn->pmtud.effective_pmtu == 0) {
+  if(!conn || conn->pmtud.effective_pmtu == 0 || conn->pmtud.state != HE_PMTUD_STATE_SEARCH_COMPLETE) {
     return HE_MAX_MTU;
   }
   return conn->pmtud.effective_pmtu;
diff --git a/src/he/flow.c b/src/he/flow.c
index a12b9d3..3a2ba95 100644
--- a/src/he/flow.c
+++ b/src/he/flow.c
@@ -35,8 +35,7 @@
 #include <wolfssl/wolfcrypt/settings.h>
 
 bool he_internal_flow_should_fragment(he_conn_t *conn, uint16_t effective_pmtu, uint16_t length) {
-  return conn->connection_type == HE_CONNECTION_TYPE_DATAGRAM &&
-         conn->pmtud.state == HE_PMTUD_STATE_SEARCH_COMPLETE && length > effective_pmtu;
+  return conn->connection_type == HE_CONNECTION_TYPE_DATAGRAM && length > effective_pmtu;
 }
 
 he_return_code_t he_conn_inside_packet_received(he_conn_t *conn, uint8_t *packet, size_t length) {
@@ -70,11 +69,9 @@ he_return_code_t he_conn_inside_packet_received(he_conn_t *conn, uint8_t *packet
   // Clamp the MSS if PMTU has been fixed
   he_return_code_t ret = HE_SUCCESS;
   uint16_t effective_pmtu = he_conn_get_effective_pmtu(conn);
-  if(conn->pmtud.state == HE_PMTUD_STATE_SEARCH_COMPLETE) {
-    ret = he_internal_clamp_mss(packet, length, effective_pmtu - HE_MSS_OVERHEAD);
-    if(ret != HE_SUCCESS) {
-      return ret;
-    }
+  ret = he_internal_clamp_mss(packet, length, effective_pmtu - HE_MSS_OVERHEAD);
+  if(ret != HE_SUCCESS) {
+    return ret;
   }
 
   // Process the packet with plugins.
diff --git a/src/he/he_internal.h b/src/he/he_internal.h
index 844deb4..d76eb1e 100644
--- a/src/he/he_internal.h
+++ b/src/he/he_internal.h
@@ -146,7 +146,7 @@ typedef struct he_internal_pmtud_ {
   he_pmtud_state_t state;
 
   /// Current effective PMTU
-  uint16_t effective_pmtu;
+  _Atomic uint16_t effective_pmtu;
 
   /// PMTUD internal data
   uint16_t base;
diff --git a/test/he/test_conn.c b/test/he/test_conn.c
index cfd7548..23833d1 100644
--- a/test/he/test_conn.c
+++ b/test/he/test_conn.c
@@ -1759,14 +1759,22 @@ void test_he_conn_start_pmtu_discovery_callback_not_set(void) {
   TEST_ASSERT_EQUAL(HE_ERR_PMTUD_CALLBACKS_NOT_SET, he_conn_start_pmtu_discovery(&conn));
 }
 
-void test_he_conn_get_effective_pmtu(void) {
+void test_he_conn_get_effective_pmtu_after_complete(void) {
   TEST_ASSERT_EQUAL(HE_MAX_MTU, he_conn_get_effective_pmtu(NULL));
   TEST_ASSERT_EQUAL(HE_MAX_MTU, he_conn_get_effective_pmtu(&conn));
 
+  conn.pmtud.state = HE_PMTUD_STATE_SEARCH_COMPLETE;
   conn.pmtud.effective_pmtu = 1212;
   TEST_ASSERT_EQUAL(1212, he_conn_get_effective_pmtu(&conn));
 }
 
+void test_he_conn_get_effective_pmtu_before_complete(void) {
+  TEST_ASSERT_EQUAL(HE_MAX_MTU, he_conn_get_effective_pmtu(NULL));
+  TEST_ASSERT_EQUAL(HE_MAX_MTU, he_conn_get_effective_pmtu(&conn));
+
+  conn.pmtud.effective_pmtu = 1212;
+  TEST_ASSERT_EQUAL(1350, he_conn_get_effective_pmtu(&conn));
+}
 void test_he_conn_pmtud_probe_timeout(void) {
   TEST_ASSERT_EQUAL(HE_ERR_NULL_POINTER, he_conn_pmtud_probe_timeout(NULL));
 
diff --git a/test/he/test_flow.c b/test/he/test_flow.c
index a40cbe0..e14d7f1 100644
--- a/test/he/test_flow.c
+++ b/test/he/test_flow.c
@@ -145,6 +145,8 @@ void test_inside_pkt_good_packet(void) {
   he_internal_is_ipv4_packet_valid_ExpectAndReturn(fake_ipv4_packet, sizeof(fake_ipv4_packet),
                                                    true);
   he_conn_get_effective_pmtu_ExpectAndReturn(conn, 1350);
+  he_internal_clamp_mss_ExpectAndReturn(fake_ipv4_packet, sizeof(fake_ipv4_packet),
+                                        1350 - HE_MSS_OVERHEAD, HE_SUCCESS);
   he_plugin_ingress_ExpectAnyArgsAndReturn(HE_SUCCESS);
   he_internal_calculate_data_packet_length_ExpectAndReturn(conn, sizeof(fake_ipv4_packet), 1242);
   he_internal_send_message_ExpectAndReturn(conn, NULL, 1242 + sizeof(he_msg_data_t), HE_SUCCESS);
@@ -164,6 +166,8 @@ void test_inside_pkt_good_packet_with_legacy_behaviour(void) {
   conn->protocol_version.minor_version = 0;
 
   he_conn_get_effective_pmtu_ExpectAndReturn(conn, 1350);
+  he_internal_clamp_mss_ExpectAndReturn(fake_ipv4_packet, sizeof(fake_ipv4_packet),
+                                        1350 - HE_MSS_OVERHEAD, HE_SUCCESS);
   he_internal_calculate_data_packet_length_ExpectAndReturn(conn, sizeof(fake_ipv4_packet), 1242);
   he_internal_send_message_ExpectAndReturn(conn, NULL, 1242 + sizeof(he_msg_data_t), HE_SUCCESS);
   he_internal_send_message_IgnoreArg_message();
@@ -178,11 +182,6 @@ void test_he_internal_flow_should_fragment(void) {
   conn->connection_type = HE_CONNECTION_TYPE_STREAM;
   TEST_ASSERT_FALSE(he_internal_flow_should_fragment(conn, 1200, 1350));
 
-  // Don't frag if PMTUD search hasn't completed
-  conn->connection_type = HE_CONNECTION_TYPE_DATAGRAM;
-  conn->pmtud.state = HE_PMTUD_STATE_SEARCHING;
-  TEST_ASSERT_FALSE(he_internal_flow_should_fragment(conn, 1200, 1350));
-
   // Don't frag if the packet length is exactly effective_pmtu
   conn->connection_type = HE_CONNECTION_TYPE_DATAGRAM;
   conn->pmtud.state = HE_PMTUD_STATE_SEARCH_COMPLETE;
@@ -227,6 +226,8 @@ void test_inside_pkt_plugin_drop(void) {
   he_internal_is_ipv4_packet_valid_ExpectAndReturn(fake_ipv4_packet, sizeof(fake_ipv4_packet),
                                                    true);
   he_conn_get_effective_pmtu_ExpectAndReturn(conn, 1350);
+  he_internal_clamp_mss_ExpectAndReturn(fake_ipv4_packet, sizeof(fake_ipv4_packet),
+                                        1350 - HE_MSS_OVERHEAD, HE_SUCCESS);
   he_plugin_ingress_ExpectAnyArgsAndReturn(HE_ERR_PLUGIN_DROP);
 
   he_return_code_t res1 =
@@ -241,6 +242,8 @@ void test_inside_pkt_plugin_fail(void) {
   he_internal_is_ipv4_packet_valid_ExpectAndReturn(fake_ipv4_packet, sizeof(fake_ipv4_packet),
                                                    true);
   he_conn_get_effective_pmtu_ExpectAndReturn(conn, 1350);
+  he_internal_clamp_mss_ExpectAndReturn(fake_ipv4_packet, sizeof(fake_ipv4_packet),
+                                        1350 - HE_MSS_OVERHEAD, HE_SUCCESS);
   he_plugin_ingress_ExpectAnyArgsAndReturn(HE_ERR_FAILED);
 
   he_return_code_t res1 =
@@ -255,6 +258,8 @@ void test_inside_pkt_plugin_overflow_fail(void) {
   he_internal_is_ipv4_packet_valid_ExpectAndReturn(fake_ipv4_packet, sizeof(fake_ipv4_packet),
                                                    true);
   he_conn_get_effective_pmtu_ExpectAndReturn(conn, 1350);
+  he_internal_clamp_mss_ExpectAndReturn(fake_ipv4_packet, sizeof(fake_ipv4_packet),
+                                        1350 - HE_MSS_OVERHEAD, HE_SUCCESS);
   he_plugin_ingress_Stub(stub_overflow_plugin);
 
   he_return_code_t res1 =
@@ -269,7 +274,9 @@ void test_inside_pkt_plugin_large_mtu(void) {
   conn->outside_mtu = 9000;
 
   he_internal_is_ipv4_packet_valid_ExpectAndReturn(buffer, sizeof(buffer), true);
-  he_conn_get_effective_pmtu_ExpectAndReturn(conn, 1350);
+  he_conn_get_effective_pmtu_ExpectAndReturn(conn, 9000);
+  he_internal_clamp_mss_ExpectAndReturn(buffer, sizeof(buffer),
+                                        9000 - HE_MSS_OVERHEAD, HE_SUCCESS);
   he_plugin_ingress_ExpectAnyArgsAndReturn(HE_SUCCESS);
 
   he_return_code_t res1 = he_conn_inside_packet_received(conn, buffer, sizeof(buffer));