diff --git a/testing/fuzzing/fuzz_support.cc b/testing/fuzzing/fuzz_support.cc
index 904d542494..1110d3afaa 100644
--- a/testing/fuzzing/fuzz_support.cc
+++ b/testing/fuzzing/fuzz_support.cc
@@ -58,14 +58,14 @@ static int recv_common(Fuzz_Data &input, uint8_t *buf, size_t buf_len)
     if (fuzz_len == 0xffff) {
         errno = EWOULDBLOCK;
         if (Fuzz_Data::FUZZ_DEBUG) {
-            std::printf("recvfrom: no data for tox1\n");
+            std::fprintf(stderr, "recvfrom: no data for tox1 (errno=%d)\n", errno);
         }
         return -1;
     }
 
     if (Fuzz_Data::FUZZ_DEBUG) {
-        std::printf(
-            "recvfrom: %zu (%02x, %02x) for tox1\n", fuzz_len, input.data()[-2], input.data()[-1]);
+        std::fprintf(
+            stderr, "recvfrom: %zu (%02x, %02x) for tox1\n", fuzz_len, input.data()[-2], input.data()[-1]);
     }
     const size_t res = std::min(buf_len, std::min(fuzz_len, input.size()));
 
@@ -120,10 +120,14 @@ static constexpr Network_Funcs fuzz_network_funcs = {
     /* .listen = */ ![](Fuzz_System *self, Socket sock, int backlog) { return 0; },
     /* .connect = */ ![](Fuzz_System *self, Socket sock, const Network_Addr *addr) { return 0; },
     /* .recvbuf = */
-    ![](Fuzz_System *self, Socket sock) {
+    ![](Fuzz_System *self, Socket sock, uint16_t length) {
         assert(sock.value == 42 || sock.value == 1337);
-        const size_t count = random_u16(self->rng.get());
-        return static_cast<int>(std::min(count, self->data.size()));
+        const size_t count = std::max(length, random_u16(self->rng.get()));
+        const int bufsize = static_cast<int>(std::min(count, self->data.size()));
+        if (Fuzz_Data::FUZZ_DEBUG) {
+            std::printf("recvbuf: %d (length=%u, count=%zu, data->size=%zu)\n", bufsize, length, count, self->data.size());
+        }
+        return bufsize;
     },
     /* .recv = */
     ![](Fuzz_System *self, Socket sock, uint8_t *buf, size_t len) {
@@ -261,7 +265,7 @@ static constexpr Network_Funcs null_network_funcs = {
     /* .bind = */ ![](Null_System *self, Socket sock, const Network_Addr *addr) { return 0; },
     /* .listen = */ ![](Null_System *self, Socket sock, int backlog) { return 0; },
     /* .connect = */ ![](Null_System *self, Socket sock, const Network_Addr *addr) { return 0; },
-    /* .recvbuf = */ ![](Null_System *self, Socket sock) { return 0; },
+    /* .recvbuf = */ ![](Null_System *self, Socket sock, uint16_t length) { return 0; },
     /* .recv = */
     ![](Null_System *self, Socket sock, uint8_t *buf, size_t len) {
         // Always fail.
@@ -378,7 +382,7 @@ static constexpr Network_Funcs record_network_funcs = {
     },
     /* .listen = */ ![](Record_System *self, Socket sock, int backlog) { return 0; },
     /* .connect = */ ![](Record_System *self, Socket sock, const Network_Addr *addr) { return 0; },
-    /* .recvbuf = */ ![](Record_System *self, Socket sock) { return 0; },
+    /* .recvbuf = */ ![](Record_System *self, Socket sock, uint32_t length) { return 0; },
     /* .recv = */
     ![](Record_System *self, Socket sock, uint8_t *buf, size_t len) {
         // Always fail.
diff --git a/toxcore/BUILD.bazel b/toxcore/BUILD.bazel
index 1f2549fac7..abb1a3b5a3 100644
--- a/toxcore/BUILD.bazel
+++ b/toxcore/BUILD.bazel
@@ -688,6 +688,19 @@ cc_library(
     ],
 )
 
+cc_fuzz_test(
+    name = "TCP_server_fuzz_test",
+    size = "small",
+    testonly = True,
+    srcs = ["TCP_server_fuzz_test.cc"],
+    # corpus = ["//tools/toktok-fuzzer/corpus:TCP_server_fuzz_test"],
+    deps = [
+        ":TCP_server",
+        "//c-toxcore/testing/fuzzing:fuzz_support",
+        "//c-toxcore/testing/fuzzing:fuzz_tox",
+    ],
+)
+
 cc_library(
     name = "TCP_client",
     srcs = ["TCP_client.c"],
@@ -779,7 +792,6 @@ cc_fuzz_test(
     deps = [
         ":DHT",
         ":TCP_client",
-        ":mem_test_util",
         ":net_crypto",
         ":network",
         "//c-toxcore/testing/fuzzing:fuzz_support",
diff --git a/toxcore/TCP_client.c b/toxcore/TCP_client.c
index 1982412cda..7e5417ef4e 100644
--- a/toxcore/TCP_client.c
+++ b/toxcore/TCP_client.c
@@ -181,7 +181,7 @@ static int proxy_http_read_connection_response(const Logger *logger, const TCP_C
 
     if (strstr((const char *)data, success) != nullptr) {
         // drain all data
-        uint16_t data_left = net_socket_data_recv_buffer(tcp_conn->con.ns, tcp_conn->con.sock);
+        uint16_t data_left = net_socket_data_recv_buffer(tcp_conn->con.ns, tcp_conn->con.sock, 0);
 
         while (data_left > 0) {
             uint8_t temp_data[16];
diff --git a/toxcore/TCP_common.c b/toxcore/TCP_common.c
index 1a8a5d9731..5a15dfa7a0 100644
--- a/toxcore/TCP_common.c
+++ b/toxcore/TCP_common.c
@@ -207,21 +207,25 @@ int write_packet_tcp_secure_connection(const Logger *logger, TCP_Connection *con
 int read_tcp_packet(
     const Logger *logger, const Memory *mem, const Network *ns, Socket sock, uint8_t *data, uint16_t length, const IP_Port *ip_port)
 {
-    const uint16_t count = net_socket_data_recv_buffer(ns, sock);
+    const uint16_t count = net_socket_data_recv_buffer(ns, sock, length);
+
+    if (count == 0) {
+        // This is a very common case. Don't log here to avoid spamming the logs.
+        return -1;
+    }
 
     if (count < length) {
-        if (count != 0) {
-            // Only log when there are some bytes available, as empty buffer
-            // is a very common case and this spams our logs.
-            LOGGER_TRACE(logger, "recv buffer has %d bytes, but requested %d bytes", count, length);
-        }
+        LOGGER_TRACE(logger, "recv buffer has %d bytes, but requested %d bytes", count, length);
         return -1;
     }
 
+    LOGGER_INFO(logger, "recv buffer has %d bytes", count);
+
     const int len = net_recv(ns, logger, sock, data, length, ip_port);
 
     if (len != length) {
-        LOGGER_ERROR(logger, "FAIL recv packet");
+        Net_Strerror error_str;
+        LOGGER_ERROR(logger, "FAIL recv packet: %d != %d (%s)", len, length, net_strerror(net_error(), &error_str));
         return -1;
     }
 
@@ -238,7 +242,7 @@ int read_tcp_packet(
 non_null()
 static uint16_t read_tcp_length(const Logger *logger, const Network *ns, Socket sock, const IP_Port *ip_port)
 {
-    const uint16_t count = net_socket_data_recv_buffer(ns, sock);
+    const uint16_t count = net_socket_data_recv_buffer(ns, sock, sizeof(uint16_t));
 
     if (count >= sizeof(uint16_t)) {
         uint8_t length_buf[sizeof(uint16_t)];
diff --git a/toxcore/TCP_server.c b/toxcore/TCP_server.c
index 288cd94c48..8e797a8d14 100644
--- a/toxcore/TCP_server.c
+++ b/toxcore/TCP_server.c
@@ -13,6 +13,10 @@
 #include <sys/ioctl.h>
 #endif /* !WIN32 */
 
+#if defined(FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION) && defined(TCP_SERVER_USE_EPOLL)
+#undef TCP_SERVER_USE_EPOLL
+#endif
+
 #ifdef TCP_SERVER_USE_EPOLL
 #include <sys/epoll.h>
 #include <unistd.h>
diff --git a/toxcore/TCP_server.h b/toxcore/TCP_server.h
index bd4c98b0cd..273ee7fa07 100644
--- a/toxcore/TCP_server.h
+++ b/toxcore/TCP_server.h
@@ -19,6 +19,10 @@
 #include "network.h"
 #include "onion.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #define MAX_INCOMING_CONNECTIONS 256
 
 #define TCP_MAX_BACKLOG MAX_INCOMING_CONNECTIONS
@@ -60,4 +64,8 @@ void kill_tcp_server(TCP_Server *tcp_server);
 nullable(1)
 const Net_Profile *tcp_server_get_net_profile(const TCP_Server *tcp_server);
 
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
 #endif /* C_TOXCORE_TOXCORE_TCP_SERVER_H */
diff --git a/toxcore/TCP_server_fuzz_test.cc b/toxcore/TCP_server_fuzz_test.cc
new file mode 100644
index 0000000000..e733f73f03
--- /dev/null
+++ b/toxcore/TCP_server_fuzz_test.cc
@@ -0,0 +1,95 @@
+#include "TCP_server.h"
+
+#include <stdio.h>
+
+#include <cassert>
+#include <cstring>
+#include <functional>
+#include <memory>
+#include <optional>
+
+#include "../testing/fuzzing/fuzz_support.hh"
+#include "../testing/fuzzing/fuzz_tox.hh"
+#include "c-toxcore/toxcore/logger.h"
+
+namespace {
+
+std::optional<std::tuple<IP_Port, uint8_t>> prepare(Fuzz_Data &input)
+{
+    IP_Port ipp;
+    ip_init(&ipp.ip, true);
+    ipp.port = 33445;
+
+    CONSUME_OR_RETURN_VAL(const uint8_t *iterations_packed, input, 1, std::nullopt);
+    const uint8_t iterations = *iterations_packed;
+
+    return {{ipp, iterations}};
+}
+
+void TestTcpServer(Fuzz_Data &input)
+{
+    const auto prep = prepare(input);
+    if (!prep.has_value()) {
+        return;
+    }
+    const auto [ipp, iterations] = prep.value();
+
+    // rest of the fuzz data is input for network
+    Null_System null_sys;
+    Fuzz_System sys(input);
+
+    const Ptr<Logger> logger(logger_new(sys.mem.get()), logger_kill);
+    if (logger == nullptr) {
+        return;
+    }
+
+#if 1
+    logger_callback_log(
+        logger.get(),
+        [](void *context, Logger_Level level, const char *file, uint32_t line, const char *func,
+            const char *message, void *userdata) {
+            if (level <= LOGGER_LEVEL_DEBUG) {
+                return;
+            }
+            fprintf(stderr, "[%s] %s\n", logger_level_to_string(level), message);
+        },
+        nullptr, nullptr);
+#endif
+
+    const std::unique_ptr<Mono_Time, std::function<void(Mono_Time *)>> mono_time(
+        mono_time_new(
+            sys.mem.get(), [](void *user_data) { return *static_cast<uint64_t *>(user_data); },
+            &sys.clock),
+        [mem = sys.mem.get()](Mono_Time *ptr) { mono_time_free(mem, ptr); });
+    if (mono_time == nullptr) {
+        return;
+    }
+
+    const uint8_t secret_key[CRYPTO_SECRET_KEY_SIZE] = {0};
+    const Ptr<TCP_Server> tcp_server(
+        new_tcp_server(logger.get(), null_sys.mem.get(), sys.rng.get(), sys.ns.get(), false, 1,
+            &ipp.port, secret_key, nullptr, nullptr),
+        kill_tcp_server);
+    if (tcp_server == nullptr) {
+        abort();
+    }
+
+    for (uint8_t i = 0; i < iterations; ++i) {
+        do_tcp_server(tcp_server.get(), mono_time.get());
+        // "Sleep"
+        sys.clock += System::BOOTSTRAP_ITERATION_INTERVAL;
+
+        if (input.empty()) {
+            break;
+        }
+    }
+}
+
+}  // namespace
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+    fuzz_select_target<TestTcpServer>(data, size);
+    return 0;
+}
diff --git a/toxcore/logger.c b/toxcore/logger.c
index b97ef8e184..e36ef31f5c 100644
--- a/toxcore/logger.c
+++ b/toxcore/logger.c
@@ -17,6 +17,24 @@
 #include "ccompat.h"
 #include "mem.h"
 
+const char *logger_level_to_string(Logger_Level level)
+{
+    switch (level) {
+    case LOGGER_LEVEL_TRACE:
+        return "LOGGER_LEVEL_TRACE";
+    case LOGGER_LEVEL_DEBUG:
+        return "LOGGER_LEVEL_DEBUG";
+    case LOGGER_LEVEL_INFO:
+        return "LOGGER_LEVEL_INFO";
+    case LOGGER_LEVEL_WARNING:
+        return "LOGGER_LEVEL_WARNING";
+    case LOGGER_LEVEL_ERROR:
+        return "LOGGER_LEVEL_ERROR";
+    }
+
+    return "<invalid Logger_Level>";
+}
+
 struct Logger {
     const Memory *mem;
 
diff --git a/toxcore/logger.h b/toxcore/logger.h
index 893c21fd10..35fea1dd93 100644
--- a/toxcore/logger.h
+++ b/toxcore/logger.h
@@ -31,6 +31,8 @@ typedef enum Logger_Level {
     LOGGER_LEVEL_ERROR,
 } Logger_Level;
 
+const char *logger_level_to_string(Logger_Level level);
+
 typedef struct Logger Logger;
 
 typedef void logger_cb(void *context, Logger_Level level, const char *file, uint32_t line,
diff --git a/toxcore/network.c b/toxcore/network.c
index 17d49ed162..8723cbb81c 100644
--- a/toxcore/network.c
+++ b/toxcore/network.c
@@ -523,7 +523,7 @@ static int sys_connect(void *obj, Socket sock, const Network_Addr *addr)
 }
 
 non_null()
-static int sys_recvbuf(void *obj, Socket sock)
+static int sys_recvbuf(void *obj, Socket sock, uint16_t length)
 {
 #ifdef OS_WIN32
     u_long count = 0;
@@ -933,7 +933,9 @@ int net_recv(const Network *ns, const Logger *log,
              Socket sock, uint8_t *buf, size_t len, const IP_Port *ip_port)
 {
     const int res = ns->funcs->recv(ns->obj, sock, buf, len);
+    fprintf(stderr, "net_recv1: %d %d\n", res, errno);
     loglogdata(log, "=>T", buf, len, ip_port, res);
+    fprintf(stderr, "net_recv2: %d %d\n", res, errno);
     return res;
 }
 
@@ -2256,9 +2258,9 @@ Socket net_socket(const Network *ns, Family domain, int type, int protocol)
     return ns->funcs->socket(ns->obj, platform_domain, platform_type, platform_prot);
 }
 
-uint16_t net_socket_data_recv_buffer(const Network *ns, Socket sock)
+uint16_t net_socket_data_recv_buffer(const Network *ns, Socket sock, uint16_t length)
 {
-    const int count = ns->funcs->recvbuf(ns->obj, sock);
+    const int count = ns->funcs->recvbuf(ns->obj, sock, length);
     return (uint16_t)max_s32(0, min_s32(count, UINT16_MAX));
 }
 
diff --git a/toxcore/network.h b/toxcore/network.h
index a13c98bf6f..1f9483a75f 100644
--- a/toxcore/network.h
+++ b/toxcore/network.h
@@ -41,7 +41,7 @@ typedef Socket net_accept_cb(void *obj, Socket sock);
 typedef int net_bind_cb(void *obj, Socket sock, const Network_Addr *addr);
 typedef int net_listen_cb(void *obj, Socket sock, int backlog);
 typedef int net_connect_cb(void *obj, Socket sock, const Network_Addr *addr);
-typedef int net_recvbuf_cb(void *obj, Socket sock);
+typedef int net_recvbuf_cb(void *obj, Socket sock, uint16_t length);
 typedef int net_recv_cb(void *obj, Socket sock, uint8_t *buf, size_t len);
 typedef int net_recvfrom_cb(void *obj, Socket sock, uint8_t *buf, size_t len, Network_Addr *addr);
 typedef int net_send_cb(void *obj, Socket sock, const uint8_t *buf, size_t len);
@@ -272,11 +272,15 @@ non_null()
 Socket net_accept(const Network *ns, Socket sock);
 
 /**
- * return the size of data in the tcp recv buffer.
- * return 0 on failure.
+ * @param ns System network interface.
+ * @param sock Socket to check the recv buffer on.
+ * @param length Length hint: how much does the caller expect to find?
+ *   This does nothing except in fuzzing mode where it helps guide packet sizes.
+ *
+ * @return the size of data in the tcp recv buffer or 0 on failure.
  */
 non_null()
-uint16_t net_socket_data_recv_buffer(const Network *ns, Socket sock);
+uint16_t net_socket_data_recv_buffer(const Network *ns, Socket sock, uint16_t length);
 
 /** Convert values between host and network byte order. */
 uint32_t net_htonl(uint32_t hostlong);