diff --git a/include/wx/compiler.h b/include/wx/compiler.h
index 5ad4df8561..de67477f84 100644
--- a/include/wx/compiler.h
+++ b/include/wx/compiler.h
@@ -139,15 +139,11 @@
    maj.min
  */
 
-/* Check for Mingw runtime version: */
+/*
+    Define Mingw identification symbols, wxCHECK_MINGW32_VERSION() is defined in
+    wx/msw/gccpriv.h which is included later, see comments there.
+ */
 #ifdef __MINGW32__
-    /* Include the header defining __MINGW32_{MAJ,MIN}OR_VERSION */
-    #include <_mingw.h>
-
-    #define wxCHECK_MINGW32_VERSION( major, minor ) \
- ( ( ( __MINGW32_MAJOR_VERSION > (major) ) \
-      || ( __MINGW32_MAJOR_VERSION == (major) && __MINGW32_MINOR_VERSION >= (minor) ) ) )
-
 /*
     MinGW-w64 project provides compilers for both Win32 and Win64 but only
     defines the same __MINGW32__ symbol for the former as MinGW32 toolchain
@@ -169,8 +165,6 @@
 #           define __MINGW32_TOOLCHAIN__
 #       endif
 #   endif
-#else
-    #define wxCHECK_MINGW32_VERSION( major, minor ) (0)
 #endif
 
 #endif // _WX_COMPILER_H_
diff --git a/include/wx/msw/gccpriv.h b/include/wx/msw/gccpriv.h
index 31453015b2..4bebc12090 100644
--- a/include/wx/msw/gccpriv.h
+++ b/include/wx/msw/gccpriv.h
@@ -17,8 +17,29 @@
     #define __GNUWIN32__
 #endif
 
-#if defined(__MINGW32__) && ( ( __GNUC__ > 2 ) || ( ( __GNUC__ == 2 ) && ( __GNUC_MINOR__ >= 95 ) ) )
+#if defined(__MINGW32__)
+    /*
+        Include the header defining __MINGW32_{MAJ,MIN}OR_VERSION but check
+        that UNICODE or _UNICODE is already defined, as _mingw.h relies on them
+        being set and we'd get weird compilation errors later if it is included
+        without them being defined, better give a clearer error right now.
+     */
+    #if !defined(UNICODE)
+        #ifndef wxUSE_UNICODE
+            #error "wxUSE_UNICODE must be defined before including this header."
+        #endif
+        #if wxUSE_UNICODE
+            #error "UNICODE must be defined before including this header."
+        #endif
+    #endif
+
     #include <_mingw.h>
+
+    #define wxCHECK_MINGW32_VERSION( major, minor ) \
+ ( ( ( __MINGW32_MAJOR_VERSION > (major) ) \
+      || ( __MINGW32_MAJOR_VERSION == (major) && __MINGW32_MINOR_VERSION >= (minor) ) ) )
+#else
+    #define wxCHECK_MINGW32_VERSION( major, minor ) (0)
 #endif
 
 #if defined( __MINGW32__ ) && !defined(__WINE__) && !defined( HAVE_W32API_H )
diff --git a/include/wx/platform.h b/include/wx/platform.h
index 97c669f7a4..1b5a4b7ffa 100644
--- a/include/wx/platform.h
+++ b/include/wx/platform.h
@@ -456,6 +456,10 @@
 #define wxNEEDS_CHARPP
 #endif
 
+/*
+    Note that wx/msw/gccpriv.h must be included after defining UNICODE and
+    _UNICODE macros as it includes _mingw.h which relies on them being set.
+ */
 #if ( defined( __GNUWIN32__ ) || defined( __MINGW32__ ) || \
     ( defined( __CYGWIN__ ) && defined( __WINDOWS__ ) ) || \
       wxCHECK_WATCOM_VERSION(1,0) ) && \
@@ -467,6 +471,8 @@
 #else
 #    undef wxCHECK_W32API_VERSION
 #    define wxCHECK_W32API_VERSION(maj, min) (0)
+#    undef wxCHECK_MINGW32_VERSION
+#    define wxCHECK_MINGW32_VERSION( major, minor ) (0)
 #endif