diff --git a/src/saveload/saveload.cpp b/src/saveload/saveload.cpp
index 06836855da..dc611adf26 100644
--- a/src/saveload/saveload.cpp
+++ b/src/saveload/saveload.cpp
@@ -534,17 +534,22 @@ static void SlNullPointers()
  * @note This function does never return as it throws an exception to
  *       break out of all the saveload code.
  */
-void NORETURN SlError(StringID string, const char *extra_msg)
+void NORETURN SlError(StringID string, const char *extra_msg, bool already_malloced)
 {
+	char *str = NULL;
+	if (extra_msg != NULL) {
+		str = already_malloced ? const_cast<char *>(extra_msg) : stredup(extra_msg);
+	}
+
 	/* Distinguish between loading into _load_check_data vs. normal save/load. */
 	if (_sl.action == SLA_LOAD_CHECK) {
 		_load_check_data.error = string;
 		free(_load_check_data.error_data);
-		_load_check_data.error_data = (extra_msg == NULL) ? NULL : stredup(extra_msg);
+		_load_check_data.error_data = str;
 	} else {
 		_sl.error_str = string;
 		free(_sl.extra_msg);
-		_sl.extra_msg = (extra_msg == NULL) ? NULL : stredup(extra_msg);
+		_sl.extra_msg = str;
 	}
 
 	/* We have to NULL all pointers here; we might be in a state where
@@ -555,6 +560,18 @@ void NORETURN SlError(StringID string, const char *extra_msg)
 	throw std::exception();
 }
 
+/**
+ * As SlError, except that it takes a format string and additional parameters
+ */
+void CDECL NORETURN SlErrorFmt(StringID string, const char *msg, ...)
+{
+	va_list va;
+	va_start(va, msg);
+	char *str = str_vfmt(msg, va);
+	va_end(va);
+	SlError(string, str, true);
+}
+
 /**
  * Error handler for corrupt savegames. Sets everything up to show the
  * error message and to clean up the mess of a partial savegame load.
@@ -562,9 +579,21 @@ void NORETURN SlError(StringID string, const char *extra_msg)
  * @note This function does never return as it throws an exception to
  *       break out of all the saveload code.
  */
-void NORETURN SlErrorCorrupt(const char *msg)
+void NORETURN SlErrorCorrupt(const char *msg, bool already_malloced)
 {
-	SlError(STR_GAME_SAVELOAD_ERROR_BROKEN_SAVEGAME, msg);
+	SlError(STR_GAME_SAVELOAD_ERROR_BROKEN_SAVEGAME, msg, already_malloced);
+}
+
+/**
+ * As SlErrorCorruptFmt, except that it takes a format string and additional parameters
+ */
+void CDECL NORETURN SlErrorCorruptFmt(const char *msg, ...)
+{
+	va_list va;
+	va_start(va, msg);
+	char *str = str_vfmt(msg, va);
+	va_end(va);
+	SlError(STR_GAME_SAVELOAD_ERROR_BROKEN_SAVEGAME, str, true);
 }
 
 
diff --git a/src/saveload/saveload.h b/src/saveload/saveload.h
index 230203b4e7..9c1d9615f5 100644
--- a/src/saveload/saveload.h
+++ b/src/saveload/saveload.h
@@ -16,6 +16,8 @@
 #include "../strings_type.h"
 #include "extended_ver_sl.h"
 
+#include <stdarg.h>
+
 /** Save or load result codes. */
 enum SaveOrLoadResult {
 	SL_OK     = 0, ///< completed successfully
@@ -570,8 +572,10 @@ void SlGlobList(const SaveLoadGlobVarList *sldg);
 void SlArray(void *array, size_t length, VarType conv);
 void SlObject(void *object, const SaveLoad *sld);
 bool SlObjectMember(void *object, const SaveLoad *sld);
-void NORETURN SlError(StringID string, const char *extra_msg = NULL);
-void NORETURN SlErrorCorrupt(const char *msg);
+void NORETURN SlError(StringID string, const char *extra_msg = NULL, bool already_malloced = false);
+void NORETURN SlErrorCorrupt(const char *msg, bool already_malloced = false);
+void CDECL NORETURN SlErrorFmt(StringID string, const char *msg, ...) WARN_FORMAT(2, 3);
+void CDECL NORETURN SlErrorCorruptFmt(const char *msg, ...) WARN_FORMAT(1, 2);
 
 bool SaveloadCrashWithMissingNewGRFs();
 
diff --git a/src/string.cpp b/src/string.cpp
index 6bc9319c1c..4bcd0cf805 100644
--- a/src/string.cpp
+++ b/src/string.cpp
@@ -131,6 +131,16 @@ char *stredup(const char *s, const char *last)
 	return tmp;
 }
 
+char *str_vfmt(const char *str, va_list va)
+{
+	char buf[4096];
+
+	int len = vseprintf(buf, lastof(buf), str, va);
+	char *p = MallocT<char>(len + 1);
+	memcpy(p, buf, len + 1);
+	return p;
+}
+
 /**
  * Format, "printf", into a newly allocated string.
  * @param str The formatting string.
@@ -138,15 +148,11 @@ char *stredup(const char *s, const char *last)
  */
 char *CDECL str_fmt(const char *str, ...)
 {
-	char buf[4096];
 	va_list va;
-
 	va_start(va, str);
-	int len = vseprintf(buf, lastof(buf), str, va);
+	char *output = str_vfmt(str, va);
 	va_end(va);
-	char *p = MallocT<char>(len + 1);
-	memcpy(p, buf, len + 1);
-	return p;
+	return output;
 }
 
 /**
diff --git a/src/string_func.h b/src/string_func.h
index ff12f3747a..dd9b42600d 100644
--- a/src/string_func.h
+++ b/src/string_func.h
@@ -39,6 +39,7 @@ int CDECL seprintf(char *str, const char *last, const char *format, ...) WARN_FO
 int CDECL vseprintf(char *str, const char *last, const char *format, va_list ap);
 
 char *CDECL str_fmt(const char *str, ...) WARN_FORMAT(1, 2);
+char *str_vfmt(const char *str, va_list ap);
 
 void str_validate(char *str, const char *last, StringValidationSettings settings = SVS_REPLACE_WITH_QUESTION_MARK);
 void ValidateString(const char *str);