diff --git a/functions.h b/functions.h
--- a/functions.h
+++ b/functions.h
@@ -275,7 +275,6 @@ void CheckConfig(void);
 int ttd_main(int argc, char* argv[]);
 
 void DeterminePaths(void);
-char * CDECL str_fmt(const char *str, ...);
 
 void bubblesort(void *base, size_t nmemb, size_t size, int(*compar)(const void *, const void *));
 bool CreateOTTDThread(void *func, void *param);
diff --git a/openttd.c b/openttd.c
--- a/openttd.c
+++ b/openttd.c
@@ -93,22 +93,6 @@ void CDECL ShowInfoF(const char *str, ..
 	ShowInfo(buf);
 }
 
-char * CDECL str_fmt(const char *str, ...)
-{
-	char buf[4096];
-	va_list va;
-	int len;
-	char *p;
-
-	va_start(va, str);
-	len = vsprintf(buf, str, va);
-	va_end(va);
-	p = malloc(len + 1);
-	if (p)
-		memcpy(p, buf, len + 1);
-	return p;
-}
-
 
 void *ReadFileToMem(const char *filename, size_t *lenp, size_t maxsize)
 {
diff --git a/string.c b/string.c
--- a/string.c
+++ b/string.c
@@ -3,6 +3,8 @@
 #include "stdafx.h"
 #include "string.h"
 
+#include <stdarg.h>
+
 void ttd_strlcat(char *dst, const char *src, size_t size)
 {
 	assert(size > 0);
@@ -39,3 +41,19 @@ char* strecpy(char* dst, const char* src
 	*dst = '\0';
 	return dst;
 }
+
+
+char* CDECL str_fmt(const char* str, ...)
+{
+	char buf[4096];
+	va_list va;
+	int len;
+	char* p;
+
+	va_start(va, str);
+	len = vsprintf(buf, str, va);
+	va_end(va);
+	p = malloc(len + 1);
+	if (p != NULL) memcpy(p, buf, len + 1);
+	return p;
+}
diff --git a/string.h b/string.h
--- a/string.h
+++ b/string.h
@@ -23,4 +23,6 @@ void ttd_strlcpy(char *dst, const char *
 char* strecat(char* dst, const char* src, const char* last);
 char* strecpy(char* dst, const char* src, const char* last);
 
+char* CDECL str_fmt(const char* str, ...);
+
 #endif