diff --git a/.devel/sphinx/alphamarek.py b/.devel/sphinx/alphamarek.py
index 7d21a974..c99e5ce7 100644
--- a/.devel/sphinx/alphamarek.py
+++ b/.devel/sphinx/alphamarek.py
@@ -113,7 +113,7 @@ def get_book_template(self, e):
             self.format_btitle(e, 'title'),
             self.format_volume_and_series(e),
             sentence [
-                field('publisher'),
+                optional_field('publisher'),
                 optional_field('address'),
                 self.format_edition(e)
             ],
diff --git a/DESCRIPTION b/DESCRIPTION
index 7fa0d3a1..ed225d65 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,6 +1,6 @@
 Package: stringi
-Version: 1.8.4
-Date: 2024-05-06
+Version: 1.8.4.9001
+Date: 2024-06-13
 Title: Fast and Portable Character String Processing Facilities
 Description: A collection of character string/text/natural language
     processing tools for pattern searching (e.g., with 'Java'-like regular
diff --git a/NEWS b/NEWS
index 8c1d2310..3d41ca19 100644
--- a/NEWS
+++ b/NEWS
@@ -1,6 +1,11 @@
 # Changelog
 
 
+## 1.8.4.9xxx (under development)
+
+* [BUGFIX] #512: Fixed PROTECT stack imbalance in `stri_encode_from_marked`.
+
+
 ## 1.8.4 (2024-05-06)
 
 * [BUILD TIME] [BUGFIX] #508: Fixed build errors on Windows
diff --git a/src/stri_encoding_conversion.cpp b/src/stri_encoding_conversion.cpp
index 486ad584..c65fccc7 100644
--- a/src/stri_encoding_conversion.cpp
+++ b/src/stri_encoding_conversion.cpp
@@ -445,13 +445,16 @@ SEXP stri_enc_toascii(SEXP str)
  * @version 0.1-?? (Marek Gagolewski, 2013-11-12)
  *
  * @version 0.2-1 (Marek Gagolewski, 2014-03-28)
- *          use StriUcnv
+ *     use StriUcnv
  *
  * @version 0.2-1 (Marek Gagolewski, 2014-04-01)
- *          calc required buf size a priori
+ *     calc required buf size a priori
  *
  * @version 0.3-1 (Marek Gagolewski, 2014-11-04)
- *    Issue #112: str_prepare_arg* retvals were not PROTECTed from gc
+ *     #112: str_prepare_arg* retvals were not PROTECTed from gc
+ *
+ * @version 1.8.4.9001 (Marek Gagolewski, 2024-06-13)
+ *     #512: Fixed PROTECT stack imbalance in `stri_encode_from_marked`.
  */
 SEXP stri_encode_from_marked(SEXP str, SEXP to, SEXP to_raw)
 {
@@ -459,12 +462,16 @@ SEXP stri_encode_from_marked(SEXP str, SEXP to, SEXP to_raw)
     const char* selected_to   = stri__prepare_arg_enc(to, "to", true); /* this is R_alloc'ed */
     bool to_raw_logical = stri__prepare_arg_logical_1_notNA(to_raw, "to_raw");
 
-    STRI__ERROR_HANDLER_BEGIN(1)
     R_len_t str_n = LENGTH(str);
+    if (str_n <= 0) {
+        UNPROTECT(1);
+        return Rf_allocVector(to_raw_logical?VECSXP:STRSXP, 0);
+    }
+
+    STRI__ERROR_HANDLER_BEGIN(1)
     StriContainerUTF16 str_cont(str, str_n);
 
     // get the number of strings to convert; if == 0, then you know what's the result
-    if (str_n <= 0) return Rf_allocVector(to_raw_logical?VECSXP:STRSXP, 0);
 
     // Open converters
     StriUcnv ucnv(selected_to);