diff --git a/docs/rh-log.txt b/docs/rh-log.txt
index 690ece343..f497a0ac8 100644
--- a/docs/rh-log.txt
+++ b/docs/rh-log.txt
@@ -1,4 +1,9 @@
-June 7, 2009  (Changes by Graf Zahl)
+June 8, 2009
+- Fixed: The RAWINPUT buffer that GetRawInputData() fills in is 40 bytes on
+  Win32 but 48 bytes on Win64, so Raw Mouse on x64 builds was getting random
+  data off the stack because I also interpreted the error return incorrectly.
+
+June 7, 2009  (Changes by Graf Zahl)
 - added parameter to A_FadeOut so that removing the actor can be made an option.
 - added PERSISTENTPOWER and TRANSFERPOINTERS submissions by Gez.
 - fixed FORCEPAIN logic.
diff --git a/src/win32/i_mouse.cpp b/src/win32/i_mouse.cpp
index 611784a5a..9130a9d7f 100644
--- a/src/win32/i_mouse.cpp
+++ b/src/win32/i_mouse.cpp
@@ -575,12 +575,14 @@ bool FRawMouse::WndProcHook(HWND hWnd, UINT message, WPARAM wParam, LPARAM lPara
 	}
 	if (message == WM_INPUT)
 	{
-		BYTE buffer[40];
+		BYTE buffer[sizeof(RAWINPUT)];
 		UINT size = sizeof(buffer);
 		int i;
 		USHORT mask;
+		UINT gridret;
 
-		if (MyGetRawInputData((HRAWINPUT)lParam, RID_INPUT, buffer, &size, sizeof(RAWINPUTHEADER)) > 0)
+		gridret = MyGetRawInputData((HRAWINPUT)lParam, RID_INPUT, buffer, &size, sizeof(RAWINPUTHEADER));
+		if (gridret != (UINT)-1 && gridret > 0)
 		{
 			RAWINPUT *raw = (RAWINPUT *)buffer;
 			if (raw->header.dwType != RIM_TYPEMOUSE)