diff --git a/goo/gfile.cc b/goo/gfile.cc
index be75c5a6..3f05822e 100644
--- a/goo/gfile.cc
+++ b/goo/gfile.cc
@@ -599,6 +599,10 @@ Goffset GoffsetMax() {
 
 #ifdef _WIN32
 
+GooFile::GooFile(HANDLE handleA) : handle(handleA) {
+  GetFileTime(handleA, NULL, NULL, &modifiedTimeOnOpen);
+}
+
 int GooFile::read(char *buf, int n, Goffset offset) const {
   DWORD m;
   
@@ -642,6 +646,14 @@ GooFile* GooFile::open(const wchar_t *fileName) {
   return handle == INVALID_HANDLE_VALUE ? NULL : new GooFile(handle);
 }
 
+bool GooFile::modificationTimeChangedSinceOpen() const
+{
+  struct _FILETIME lastModified;
+  GetFileTime(handle, NULL, NULL, &lastModified);
+
+  return modifiedTimeOnOpen.dwHighDateTime != lastModified.dwHighDateTime || modifiedTimeOnOpen.dwLowDateTime != lastModified.dwLowDateTime;
+}
+
 #else
 
 int GooFile::read(char *buf, int n, Goffset offset) const {
diff --git a/goo/gfile.h b/goo/gfile.h
index 233c4829..f9cc2609 100644
--- a/goo/gfile.h
+++ b/goo/gfile.h
@@ -147,11 +147,12 @@ public:
   ~GooFile() { CloseHandle(handle); }
 
   // Asuming than on windows you can't change files that are already open
-  bool modificationTimeChangedSinceOpen() const { return false; };
+  bool modificationTimeChangedSinceOpen() const;
   
 private:
-  GooFile(HANDLE handleA): handle(handleA) {}
+  GooFile(HANDLE handleA);
   HANDLE handle;
+  struct _FILETIME modifiedTimeOnOpen;
 #else
   ~GooFile() { close(fd); }