diff --git a/src/lapi.c b/src/lapi.c
index bb07ca8..cdfa967 100644
--- a/src/lapi.c
+++ b/src/lapi.c
@@ -1233,6 +1233,21 @@ LUA_API int lua_error (lua_State *L) {
   lua_lock(L);
   LUAI_TRY_BLOCK(L) {
     api_checknelems(L, 1);
+    if (!lj.previous) {
+      /* Log only when there is no outer error handler -- i.e. the error
+       * will ultimately reach the panic branch.  We check lj.previous
+       * (not L->errorJmp) because LUAI_TRY_BLOCK already set
+       * L->errorJmp = &lj, so L->errorJmp is always non-NULL here.
+       *
+       * Use raw accessors (ttisstring/svalue) instead of the public API
+       * (lua_isstring/lua_tostring).  lua_isstring returns true for
+       * numbers, and lua_tostring -> lua_tolstring calls lua_lock for
+       * number-to-string conversion, which would deadlock since we
+       * already hold the lock from lua_error's lua_lock above. */
+      StkId o = L->top - 1;
+      const char *msg = ttisstring(o) ? svalue(o) : "(non-string error)";
+      thrlua_log(L, DCRITICAL, "lua_error (unhandled): %s\n", msg);
+    }
     luaG_errormsg(L);
   } LUAI_TRY_FINALLY(L) {
     lua_unlock(L);
diff --git a/src/ldebug.c b/src/ldebug.c
index ec60a37..e17b490 100644
--- a/src/ldebug.c
+++ b/src/ldebug.c
@@ -631,6 +631,11 @@ void luaG_errormsg (lua_State *L) {
     incr_top(L);
     luaD_call(L, L->top - 2, 1);  /* call it */
   }
+  if (!L->errorJmp) {
+    const char *msg = (L->top > L->base && ttisstring(L->top - 1))
+      ? svalue(L->top - 1) : "(non-string error)";
+    thrlua_log(L, DCRITICAL, "luaG_errormsg (unhandled): %s\n", msg);
+  }
   luaD_throw(L, LUA_ERRRUN);
 }
 
diff --git a/src/ldo.c b/src/ldo.c
index a64e320..9b2db4c 100644
--- a/src/ldo.c
+++ b/src/ldo.c
@@ -69,10 +69,23 @@ void luaD_throw (lua_State *L, int errcode) {
     LUAI_THROW(L, L->errorJmp);
   }
   else {
+    thrlua_log(L, DCRITICAL,
+      "luaD_throw: no error handler, errcode=%d, L=%p, invoking panic\n",
+      errcode, (void *)L);
     L->status = cast_byte(errcode);
     if (G(L)->panic) {
       resetstack(L, errcode);
-      lua_unlock(L);
+      /* Do NOT call lua_unlock(L) here.  When luaD_throw is reached
+       * via LUAI_TRY_END re-throw, the LUAI_TRY_FINALLY block has
+       * already run and the lock state depends on the call site:
+       * some FINALLY blocks call lua_unlock (lapi.c, lauxlib.c) while
+       * others call lua_lock (ldo.c callhook/precall).  Unconditionally
+       * unlocking here caused a double-unlock that corrupted the
+       * pthread mutex on Linux/glibc, making every subsequent
+       * lua_lock() on this lua_State fail with EINVAL and abort().
+       * All direct callers of luaD_throw (lmem.c, ldebug.c, lundump.c,
+       * llex.c) always have an outer errorJmp so they never reach
+       * this panic branch. */
       G(L)->panic(L);
     }
     exit(EXIT_FAILURE);
diff --git a/src/lstrlib.c b/src/lstrlib.c
index 6693eb3..35bfd81 100644
--- a/src/lstrlib.c
+++ b/src/lstrlib.c
@@ -138,8 +138,16 @@ static int str_dump (lua_State *L) {
   luaL_checktype(L, 1, LUA_TFUNCTION);
   lua_settop(L, 1);
   luaL_buffinit(L,&b);
-  if (lua_dump(L, writer, &b) != 0)
-    luaL_error(L, "unable to dump given function");
+  if (lua_dump(L, writer, &b) != 0) {
+    lua_Debug ar;
+    lua_pushvalue(L, 1);
+    lua_getinfo(L, ">nS", &ar);
+    luaL_error(L, "unable to dump given function (%s '%s' defined at %s:%d)",
+      ar.what ? ar.what : "?",
+      ar.name ? ar.name : "(anonymous)",
+      ar.short_src ? ar.short_src : "?",
+      ar.linedefined);
+  }
   luaL_pushresult(&b);
   return 1;
 }
diff --git a/src/thrlua.h b/src/thrlua.h
index 3f39d8f..aa8a217 100644
--- a/src/thrlua.h
+++ b/src/thrlua.h
@@ -254,6 +254,16 @@ extern void lua_do_longjmp(luai_jmpbuf env, int val)
 #define LUAI_TRY_END(L) \
   (L)->errorJmp = lj.previous; \
   if (lj.status) { \
+    /* Only log when there is NO outer handler -- that is the \
+     * dangerous path that hits luaD_throw's panic branch. \
+     * Normal error propagation (with an outer handler) is \
+     * high-frequency and must not be logged. */ \
+    if (!lj.previous) { \
+      thrlua_log((L), DCRITICAL, \
+        "LUAI_TRY_END: error status=%d in TRY block at %s:%d, " \
+        "re-throwing with NO outer handler, L=%p\n", \
+        lj.status, lj.file, lj.line, (void *)(L)); \
+    } \
     luaD_throw((L), lj.status); \
   } \
 } while(0)