diff --git a/src/core/util.cpp b/src/core/util.cpp
index ff53c65fc..ce97546c9 100644
--- a/src/core/util.cpp
+++ b/src/core/util.cpp
@@ -801,7 +801,11 @@ std::vector<std::pair<std::string, float>> parse_prompt_attention(const std::str
     float round_bracket_multiplier  = 1.1f;
     float square_bracket_multiplier = 1 / 1.1f;
 
-    std::regex re_attention(R"(\\\(|\\\)|\\\[|\\\]|\\\\|\\|\(|\[|:([+-]?[.\d]+)\)|\)|\]|\bBREAK\b|[^\\()\[\]:B]+|:|\bB)");
+    // libstdc++ std::regex recurses per matched character; unbounded runs overflow
+    // the stack. Split runs are merged back by the equal-weight pass below.
+    const int max_plain_text_run = 1024;
+    std::regex re_attention(R"(\\\(|\\\)|\\\[|\\\]|\\\\|\\|\(|\[|:([+-]?[.\d]+)\)|\)|\]|\bBREAK\b|[^\\()\[\]:B]{1,)" +
+                            std::to_string(max_plain_text_run) + R"(}|:|\bB)");
     std::regex re_break(R"(\s*\bBREAK\b\s*)");
 
     auto multiply_range = [&](int start_position, float multiplier) {