diff --git a/source/core/StarException.hpp b/source/core/StarException.hpp
index 0e6a4ed..87f0571 100644
--- a/source/core/StarException.hpp
+++ b/source/core/StarException.hpp
@@ -4,9 +4,8 @@
 #include "StarMemory.hpp"
 #include "StarOutputProxy.hpp"
 
-
 #include <string>
-
+#include <sstream>
 
 namespace Star {
 
diff --git a/source/core/StarException_windows.cpp b/source/core/StarException_windows.cpp
index 8f5786f..b40df12 100644
--- a/source/core/StarException_windows.cpp
+++ b/source/core/StarException_windows.cpp
@@ -5,7 +5,6 @@
 #include "StarString_windows.hpp"
 
 #include <DbgHelp.h>
-#include <sstream>
 
 namespace Star {
 
diff --git a/source/core/StarString.cpp b/source/core/StarString.cpp
index 924c83b..86fea67 100644
--- a/source/core/StarString.cpp
+++ b/source/core/StarString.cpp
@@ -1136,7 +1136,3 @@ size_t hash<StringList>::operator()(StringList const& sl) const {
 }
 
 }
-
-fmt::v10::appender fmt::formatter<Star::String>::format(Star::String const& s, format_context& ctx) const {
-  return formatter<std::string>::format(s.utf8(), ctx);
-};
diff --git a/source/core/StarString.hpp b/source/core/StarString.hpp
index a401076..9ffe536 100644
--- a/source/core/StarString.hpp
+++ b/source/core/StarString.hpp
@@ -520,7 +520,11 @@ StringList StringList::sorted(Comparator&& comparator) const {
 }
 
 template <> struct fmt::formatter<Star::String> : formatter<std::string> {
-  fmt::v10::appender format(Star::String const& s, format_context& ctx) const;
+  auto format(Star::String const& s, format_context& ctx) const;
+};
+
+auto fmt::formatter<Star::String>::format(Star::String const& s, format_context& ctx) const {
+  return formatter<std::string>::format(s.utf8(), ctx);
 };
 
 #endif
diff --git a/source/core/StarStringView.cpp b/source/core/StarStringView.cpp
index 8090515..fa62cf5 100644
--- a/source/core/StarStringView.cpp
+++ b/source/core/StarStringView.cpp
@@ -425,8 +425,4 @@ std::ostream& operator<<(std::ostream& os, StringView const& s) {
   return os;
 }
 
-}
-
-fmt::v10::appender fmt::formatter<Star::StringView>::format(Star::StringView const& s, format_context& ctx) const {
-  return formatter<std::string_view>::format(s.utf8(), ctx);
-};
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/source/core/StarStringView.hpp b/source/core/StarStringView.hpp
index 67d654e..9193de9 100644
--- a/source/core/StarStringView.hpp
+++ b/source/core/StarStringView.hpp
@@ -116,7 +116,11 @@ private:
 }
 
 template <> struct fmt::formatter<Star::StringView> : formatter<std::string_view> {
-  fmt::v10::appender format(Star::StringView const& s, format_context& ctx) const;
+  auto format(Star::StringView const& s, format_context& ctx) const;
+};
+
+auto fmt::formatter<Star::StringView>::format(Star::StringView const& s, format_context& ctx) const {
+  return formatter<std::string_view>::format(s.utf8(), ctx);
 };
 
 #endif
\ No newline at end of file