diff --git a/source/lib/sysdep/win/win.h b/source/lib/sysdep/win/win.h
index 29323faa89..831d7c0ee8 100755
--- a/source/lib/sysdep/win/win.h
+++ b/source/lib/sysdep/win/win.h
@@ -22,13 +22,18 @@
 #error "including win.h without _WIN32 defined"
 #endif
 
+#include "config.h"
+
 #include <wchar.h>
 
-// C99
-#define snprintf _snprintf
-#define swprintf _snwprintf
-#define vsnprintf _vsnprintf
-#define vsnwprintf _vsnwprintf
+// provide C99 *snprintf functions if compiler doesn't already
+// (MinGW does, VC7.1 doesn't).
+#ifndef HAVE_C99
+# define snprintf _snprintf
+# define swprintf _snwprintf
+# define vsnprintf _vsnprintf
+# define vsnwprintf _vsnwprintf
+#endif
 
 #include <stddef.h>	// wchar_t
 
diff --git a/source/lib/sysdep/win/win_internal.h b/source/lib/sysdep/win/win_internal.h
index 028c0e0a08..d34de6af25 100755
--- a/source/lib/sysdep/win/win_internal.h
+++ b/source/lib/sysdep/win/win_internal.h
@@ -133,6 +133,9 @@ typedef struct _MEMORYSTATUSEX
 //
 ///////////////////////////////////////////////////////////////////////////////
 
+// MinGW headers are already fixed; only change on VC
+#ifdef _MSC_VER
+
 #ifndef NTSTATUS
 #define NTSTATUS long
 #endif
@@ -229,16 +232,6 @@ typedef struct {
 
 #endif	// WINVER < 0x500
 
-typedef struct _PROCESSOR_POWER_INFORMATION
-{
-	ULONG Number;
-	ULONG MaxMhz;
-	ULONG CurrentMhz;
-	ULONG MhzLimit;
-	ULONG MaxIdleState;
-	ULONG CurrentIdleState;
-} PROCESSOR_POWER_INFORMATION, *PPROCESSOR_POWER_INFORMATION;
-
 typedef struct _SYSTEM_POWER_INFORMATION
 {
 	ULONG MaxIdlenessAllowed;
@@ -251,6 +244,19 @@ typedef struct _SYSTEM_POWER_INFORMATION
 #define PO_TZ_INVALID_MODE 0 // The system does not support CPU throttling,
 	                         // or there is no thermal zone defined [..]
 
+#endif	// #ifdef _MSC_VER
+
+// neither VC7.1 nor MinGW define this
+typedef struct _PROCESSOR_POWER_INFORMATION
+{
+	ULONG Number;
+	ULONG MaxMhz;
+	ULONG CurrentMhz;
+	ULONG MhzLimit;
+	ULONG MaxIdleState;
+	ULONG CurrentIdleState;
+} PROCESSOR_POWER_INFORMATION, *PPROCESSOR_POWER_INFORMATION;
+
 
 ///////////////////////////////////////////////////////////////////////////////
 //
diff --git a/source/lib/sysdep/win/wposix.h b/source/lib/sysdep/win/wposix.h
index bc28f442b1..a48d866b92 100755
--- a/source/lib/sysdep/win/wposix.h
+++ b/source/lib/sysdep/win/wposix.h
@@ -122,7 +122,10 @@ EWOULDBLOCK    // Operation would block (may be the same value as EAGAIN]).
 // sys/stat.h
 //
 
+// already defined by MinGW
+#ifdef _MSC_VER
 typedef unsigned int mode_t;
+#endif
 
 // VC libc includes stat, but it's quite slow.
 // we implement our own, but use the CRT struct definition.
diff --git a/source/lib/sysdep/win/wposix_types.h b/source/lib/sysdep/win/wposix_types.h
index aa75070723..9d98bbe9cd 100644
--- a/source/lib/sysdep/win/wposix_types.h
+++ b/source/lib/sysdep/win/wposix_types.h
@@ -5,7 +5,12 @@
 
 typedef char int8_t;
 typedef short int16_t;
+
+// already defined by MinGW
+#ifdef _MSC_VER
 typedef int int32_t;
+#endif
+
 #if defined(_MSC_VER) || defined(__INTEL_COMPILER) || defined(__LCC__)
 typedef __int64 int64_t;
 #elif defined(__GNUC__) || defined(__MWERKS__) || defined(__SUNPRO_C) || defined(__DMC__)