diff --git a/renderdoc/os/os_specific.cpp b/renderdoc/os/os_specific.cpp
index dfe414436..07cde014c 100644
--- a/renderdoc/os/os_specific.cpp
+++ b/renderdoc/os/os_specific.cpp
@@ -50,6 +50,30 @@ int vsnprintf(char *str, size_t bufSize, const char *format, va_list args)
   return ::utf8printf(str, bufSize, format, args);
 }
 
+string Fmt(const char *format, ...)
+{
+  va_list args;
+  va_start(args, format);
+
+  va_list args2;
+  va_copy(args2, args);
+
+  int size = StringFormat::vsnprintf(NULL, 0, format, args2);
+
+  char *buf = new char[size + 1];
+  StringFormat::vsnprintf(buf, size + 1, format, args);
+  buf[size] = 0;
+
+  va_end(args);
+  va_end(args2);
+
+  string ret = buf;
+
+  delete[] buf;
+
+  return ret;
+}
+
 int Wide2UTF8(wchar_t chr, char mbchr[4])
 {
   // U+00000 -> U+00007F 1 byte  0xxxxxxx
diff --git a/renderdoc/os/os_specific.h b/renderdoc/os/os_specific.h
index 2d5e73ce7..1d6fcdf77 100644
--- a/renderdoc/os/os_specific.h
+++ b/renderdoc/os/os_specific.h
@@ -363,9 +363,6 @@ namespace StringFormat
 {
 void sntimef(char *str, size_t bufSize, const char *format);
 
-// forwards to vsnprintf below, needed to be here due to va_copy differences
-string Fmt(const char *format, ...);
-
 string Wide2UTF8(const std::wstring &s);
 };
 
@@ -376,6 +373,8 @@ namespace StringFormat
 int vsnprintf(char *str, size_t bufSize, const char *format, va_list v);
 int snprintf(char *str, size_t bufSize, const char *format, ...);
 
+string Fmt(const char *format, ...);
+
 int Wide2UTF8(wchar_t chr, char mbchr[4]);
 };
 
diff --git a/renderdoc/os/posix/posix_stringio.cpp b/renderdoc/os/posix/posix_stringio.cpp
index c5b1916ae..67c57e8c7 100644
--- a/renderdoc/os/posix/posix_stringio.cpp
+++ b/renderdoc/os/posix/posix_stringio.cpp
@@ -409,28 +409,4 @@ void sntimef(char *str, size_t bufSize, const char *format)
 
   strftime(str, bufSize, format, tmv);
 }
-
-string Fmt(const char *format, ...)
-{
-  va_list args;
-  va_start(args, format);
-
-  va_list args2;
-  va_copy(args2, args);
-
-  int size = StringFormat::vsnprintf(NULL, 0, format, args2);
-
-  char *buf = new char[size + 1];
-  StringFormat::vsnprintf(buf, size + 1, format, args);
-  buf[size] = 0;
-
-  va_end(args);
-  va_end(args2);
-
-  string ret = buf;
-
-  delete[] buf;
-
-  return ret;
-}
 };
diff --git a/renderdoc/os/win32/win32_stringio.cpp b/renderdoc/os/win32/win32_stringio.cpp
index de0f26bee..0142dc1aa 100644
--- a/renderdoc/os/win32/win32_stringio.cpp
+++ b/renderdoc/os/win32/win32_stringio.cpp
@@ -563,33 +563,6 @@ void sntimef(char *str, size_t bufSize, const char *format)
   }
 }
 
-// this function is only platform specific because va_copy isn't implemented
-// on MSVC
-string Fmt(const char *format, ...)
-{
-  va_list args;
-  va_start(args, format);
-
-  va_list args2;
-  // va_copy(args2, args); // not implemented on VS2010
-  args2 = args;
-
-  int size = StringFormat::vsnprintf(NULL, 0, format, args2);
-
-  char *buf = new char[size + 1];
-  StringFormat::vsnprintf(buf, size + 1, format, args);
-  buf[size] = 0;
-
-  va_end(args);
-  va_end(args2);
-
-  string ret = buf;
-
-  delete[] buf;
-
-  return ret;
-}
-
 string Wide2UTF8(const wstring &s)
 {
   int bytes_required = WideCharToMultiByte(CP_UTF8, 0, s.c_str(), -1, NULL, 0, NULL, NULL);