diff --git a/mk/prefix.mk b/mk/prefix.mk
index 97c9c33fb7..7ce734415b 100644
--- a/mk/prefix.mk
+++ b/mk/prefix.mk
@@ -116,7 +116,11 @@ else
 # Fix GCC 13 <cstdlib> — relibc declares but doesn't implement strtold (long double).
 # GCC was built with _GLIBCXX_USE_C99_STDLIB=1 but relibc lacks the symbol.
 # Remove 'using ::strtold' from the C++ stdlib header to prevent compile errors.
-	sed -i '/using ::strtold;/d; /using ::__gnu_cxx::strtold;/d' "$(PREFIX)/gcc-install/$(GNU_TARGET)/include/c++"/*/cstdlib 2>/dev/null || true
+# Also remove stold() from basic_string.h which references std::strtold.
+	export _GCC_CSTDLIB="$(PREFIX)/gcc-install/$(GNU_TARGET)/include/c++"/*/cstdlib; \
+	sed -i '/using ::strtold;/d; /using ::__gnu_cxx::strtold;/d' $$_GCC_CSTDLIB 2>/dev/null || true; \
+	STRHDR="$(PREFIX)/gcc-install/$(GNU_TARGET)/include/c++"/*/bits/basic_string.h; \
+	sed -i '/inline long double/,/^#endif \/\/ _GLIBCXX_USE_C99_STDLIB/{ /stold(/,/^#endif/d; }' $$STRHDR 2>/dev/null || true
 # Propagate fresh relibc artifacts to the redoxer toolchain at
 # ~/.redoxer/<target>/toolchain/.  The redoxer ships its own sysroot
 # snapshot from initial setup; without this sync the GCC driver inside