diff --git a/mdbx.h b/mdbx.h
index d15c3e1e..9c721b47 100644
--- a/mdbx.h
+++ b/mdbx.h
@@ -1012,6 +1012,7 @@ typedef void MDBX_debug_func(MDBX_log_level_t loglevel, const char *function,
 
 /** \brief The "don't change `logger`" value for mdbx_setup_debug() */
 #define MDBX_LOGGER_DONTCHANGE ((MDBX_debug_func *)(intptr_t)-1)
+#define MDBX_LOGGER_NOFMT_DONTCHANGE ((MDBX_debug_func_nofmt *)(intptr_t)-1)
 
 /** \brief Setup global log-level, debug options and debug logger.
  * \returns The previously `debug_flags` in the 0-15 bits
@@ -1020,6 +1021,17 @@ LIBMDBX_API int mdbx_setup_debug(MDBX_log_level_t log_level,
                                  MDBX_debug_flags_t debug_flags,
                                  MDBX_debug_func *logger);
 
+typedef void MDBX_debug_func_nofmt(MDBX_log_level_t loglevel,
+                                   const char *function, int line,
+                                   const char *msg,
+                                   unsigned length) MDBX_CXX17_NOEXCEPT;
+
+LIBMDBX_API int mdbx_setup_debug_nofmt(MDBX_log_level_t log_level,
+                                       MDBX_debug_flags_t debug_flags,
+                                       MDBX_debug_func_nofmt *logger,
+                                       char *logger_buffer,
+                                       size_t logger_buffer_size);
+
 /** \brief A callback function for most MDBX assert() failures,
  * called before printing the message and aborting.
  * \see mdbx_env_set_assert()
diff --git a/src/core.c b/src/core.c
index 09d6ae84..2fbf0bf2 100644
--- a/src/core.c
+++ b/src/core.c
@@ -1445,6 +1445,10 @@ __cold void thread_dtor(void *rthc) {
 #endif
 }
 
+MDBX_INTERNAL_VAR_INSTA struct mdbx_static mdbx_static = {
+    MDBX_RUNTIME_FLAGS_INIT, MDBX_LOG_FATAL, {nullptr}, 0, nullptr};
+static osal_fastmutex_t debug_lock;
+
 MDBX_EXCLUDE_FOR_GPROF
 __cold void global_dtor(void) {
   const uint32_t current_pid = osal_getpid();
@@ -1547,6 +1551,7 @@ __cold void global_dtor(void) {
 
   osal_dtor();
   TRACE("<< pid %d\n", current_pid);
+  ENSURE(nullptr, osal_fastmutex_destroy(&debug_lock) == 0);
 }
 
 __cold int rthc_register(MDBX_env *const env) {
@@ -3233,9 +3238,6 @@ static __always_inline int __must_check_result dpl_append(MDBX_txn *txn,
 
 /*----------------------------------------------------------------------------*/
 
-MDBX_INTERNAL_VAR_INSTA struct mdbx_static mdbx_static = {
-    MDBX_RUNTIME_FLAGS_INIT, MDBX_LOG_FATAL, nullptr, 0, nullptr};
-
 static __must_check_result __inline int page_retire(MDBX_cursor *mc,
                                                     MDBX_page *mp);
 
@@ -3587,9 +3589,18 @@ const char *mdbx_strerror_ANSI2OEM(int errnum) {
 
 __cold void debug_log_va(int level, const char *function, int line,
                          const char *fmt, va_list args) {
-  if (mdbx_static.logger)
-    mdbx_static.logger(level, function, line, fmt, args);
-  else {
+  ENSURE(nullptr, osal_fastmutex_acquire(&debug_lock) == 0);
+  if (mdbx_static.logger.ptr) {
+    if (mdbx_static.logger_buffer == nullptr)
+      mdbx_static.logger.fmt(level, function, line, fmt, args);
+    else {
+      const int len = vsnprintf(mdbx_static.logger_buffer,
+                                mdbx_static.logger_buffer_size, fmt, args);
+      if (len > 0)
+        mdbx_static.logger.nofmt(level, function, line,
+                                 mdbx_static.logger_buffer, len);
+    }
+  } else {
 #if defined(_WIN32) || defined(_WIN64)
     if (IsDebuggerPresent()) {
       int prefix_len = 0;
@@ -3622,6 +3633,7 @@ __cold void debug_log_va(int level, const char *function, int line,
     fflush(stderr);
 #endif
   }
+  ENSURE(nullptr, osal_fastmutex_release(&debug_lock) == 0);
 }
 
 __cold void debug_log(int level, const char *function, int line,
@@ -24621,10 +24633,12 @@ __cold MDBX_INTERNAL_FUNC int cleanup_dead_readers(MDBX_env *env,
   return rc;
 }
 
-__cold int mdbx_setup_debug(MDBX_log_level_t level, MDBX_debug_flags_t flags,
-                            MDBX_debug_func *logger) {
-  const int rc = mdbx_static.flags | (mdbx_static.loglevel << 16);
+__cold static int setup_debug(MDBX_log_level_t level, MDBX_debug_flags_t flags,
+                              union logger_union logger, char *buffer,
+                              size_t buffer_size) {
+  ENSURE(nullptr, osal_fastmutex_acquire(&debug_lock) == 0);
 
+  const int rc = mdbx_static.flags | (mdbx_static.loglevel << 16);
   if (level != MDBX_LOG_DONTCHANGE)
     mdbx_static.loglevel = (uint8_t)level;
 
@@ -24638,11 +24652,34 @@ __cold int mdbx_setup_debug(MDBX_log_level_t level, MDBX_debug_flags_t flags,
     mdbx_static.flags = (uint8_t)flags;
   }
 
-  if (logger != MDBX_LOGGER_DONTCHANGE)
-    mdbx_static.logger = logger;
+  assert(MDBX_LOGGER_DONTCHANGE == ((MDBX_debug_func *)(intptr_t)-1));
+  if (logger.ptr != (void *)((intptr_t)-1)) {
+    mdbx_static.logger.ptr = logger.ptr;
+    mdbx_static.logger_buffer = buffer;
+    mdbx_static.logger_buffer_size = buffer_size;
+  }
+
+  ENSURE(nullptr, osal_fastmutex_release(&debug_lock) == 0);
   return rc;
 }
 
+__cold int mdbx_setup_debug_nofmt(MDBX_log_level_t level,
+                                  MDBX_debug_flags_t flags,
+                                  MDBX_debug_func_nofmt *logger, char *buffer,
+                                  size_t buffer_size) {
+  union logger_union thunk;
+  thunk.nofmt =
+      (logger && buffer && buffer_size) ? logger : MDBX_LOGGER_NOFMT_DONTCHANGE;
+  return setup_debug(level, flags, thunk, buffer, buffer_size);
+}
+
+__cold int mdbx_setup_debug(MDBX_log_level_t level, MDBX_debug_flags_t flags,
+                            MDBX_debug_func *logger) {
+  union logger_union thunk;
+  thunk.fmt = logger;
+  return setup_debug(level, flags, thunk, nullptr, 0);
+}
+
 __cold static txnid_t kick_longlived_readers(MDBX_env *env,
                                              const txnid_t laggard) {
   DEBUG("DB size maxed out by reading #%" PRIaTXN, laggard);
@@ -26761,6 +26798,7 @@ __cold static void rthc_afterfork(void) {
 #endif /* ! Windows */
 
 __cold void global_ctor(void) {
+  ENSURE(nullptr, osal_fastmutex_init(&debug_lock) == 0);
   osal_ctor();
   rthc_limit = RTHC_INITIAL_LIMIT;
   rthc_table = rthc_table_static;
diff --git a/src/internals.h b/src/internals.h
index 98005f99..bb6b5e76 100644
--- a/src/internals.h
+++ b/src/internals.h
@@ -244,10 +244,16 @@ extern LIBMDBX_API const char *const mdbx_sourcery_anchor;
 #define MDBX_RUNTIME_FLAGS_INIT                                                \
   ((MDBX_DEBUG) > 0) * MDBX_DBG_ASSERT + ((MDBX_DEBUG) > 1) * MDBX_DBG_AUDIT
 
+union logger_union {
+  void *ptr;
+  MDBX_debug_func *fmt;
+  MDBX_debug_func_nofmt *nofmt;
+};
+
 MDBX_INTERNAL_VAR_PROTO struct mdbx_static {
   uint8_t flags;
   uint8_t loglevel;
-  MDBX_debug_func *logger;
+  union logger_union logger;
   size_t logger_buffer_size;
   char *logger_buffer;
 } mdbx_static;
diff --git a/src/osal.c b/src/osal.c
index 8109c749..86f93d44 100644
--- a/src/osal.c
+++ b/src/osal.c
@@ -244,7 +244,7 @@ MDBX_NORETURN __cold void assert_fail(const char *msg, const char *func,
                                       unsigned line) {
 #endif /* MDBX_DEBUG */
 
-  if (mdbx_static.logger)
+  if (mdbx_static.logger.ptr)
     debug_log(MDBX_LOG_FATAL, func, line, "assert: %s\n", msg);
   else {
 #if defined(_WIN32) || defined(_WIN64)
@@ -287,7 +287,7 @@ __cold void mdbx_panic(const char *fmt, ...) {
           ? "<troubles with panic-message preparation>"
           : message;
 
-  if (mdbx_static.logger)
+  if (mdbx_static.logger.ptr)
     debug_log(MDBX_LOG_FATAL, "panic", 0, "%s", const_message);
 
   while (1) {