diff --git a/mkspecs/features/ctest_testcase_common.prf b/mkspecs/features/ctest_testcase_common.prf
index cdc5cca1d7..15701b6a41 100644
--- a/mkspecs/features/ctest_testcase_common.prf
+++ b/mkspecs/features/ctest_testcase_common.prf
@@ -1,10 +1,5 @@
 
-win32 {
-    CMAKE_VERSION = $$system(cmake --version 2>NUL, lines)
-} else {
-    CMAKE_VERSION = $$system(cmake --version 2>/dev/null, lines)
-}
-
+CMAKE_VERSION = $$system(cmake --version 2>$$QMAKE_NULL_DEVICE, lines)
 CMAKE_VERSION = $$member(CMAKE_VERSION, 0, 0)
 
 check.commands =
@@ -15,12 +10,7 @@ isEmpty(CMAKE_VERSION) {
     return()
 }
 
-win32 {
-    CTEST_VERSION = $$system(ctest --version 2>NUL)
-} else {
-    CTEST_VERSION = $$system(ctest --version 2>/dev/null)
-}
-
+CTEST_VERSION = $$system(ctest --version 2>$$QMAKE_NULL_DEVICE)
 isEmpty(CTEST_VERSION) {
     message("ctest executable not found. Not running CMake unit tests")
     return()
diff --git a/mkspecs/features/qt_functions.prf b/mkspecs/features/qt_functions.prf
index c00fdb73f8..1f44650227 100644
--- a/mkspecs/features/qt_functions.prf
+++ b/mkspecs/features/qt_functions.prf
@@ -291,10 +291,7 @@ defineReplace(pkgConfigExecutable) {
         }
     }
 
-    equals(QMAKE_HOST.os, Windows): \
-        PKG_CONFIG += 2> NUL
-    else: \
-        PKG_CONFIG += 2> /dev/null
+    PKG_CONFIG += 2> $$QMAKE_NULL_DEVICE
 
     return($$PKG_CONFIG)
 }
diff --git a/mkspecs/features/spec_post.prf b/mkspecs/features/spec_post.prf
index f87bf3c037..62be69ffda 100644
--- a/mkspecs/features/spec_post.prf
+++ b/mkspecs/features/spec_post.prf
@@ -82,6 +82,7 @@ equals(MAKEFILE_GENERATOR, MSBUILD) \
     QMAKE_MKDIR             = mkdir          # legacy
     QMAKE_MKDIR_CMD         = if not exist %1 mkdir %1 & if not exist %1 exit 1
     QMAKE_STREAM_EDITOR     = $(QMAKE) -install sed
+    QMAKE_NULL_DEVICE       = NUL
     QMAKE_INSTALL_FILE      = copy /y
     QMAKE_INSTALL_PROGRAM   = copy /y
 } else {
@@ -101,6 +102,7 @@ equals(MAKEFILE_GENERATOR, MSBUILD) \
     QMAKE_MKDIR             = mkdir -p   # legacy
     QMAKE_MKDIR_CMD         = test -d %1 || mkdir -p %1
     QMAKE_STREAM_EDITOR     = sed
+    QMAKE_NULL_DEVICE       = /dev/null
 
     equals(QMAKE_HOST.os, Windows) {
         MINGW_IN_SHELL = 1   # legacy
diff --git a/mkspecs/features/toolchain.prf b/mkspecs/features/toolchain.prf
index 35175f1744..e7ada377d7 100644
--- a/mkspecs/features/toolchain.prf
+++ b/mkspecs/features/toolchain.prf
@@ -32,15 +32,11 @@ isEmpty($${target_prefix}.INCDIRS) {
     # Get default include and library paths from compiler
     #
     gcc {
-        !equals(QMAKE_HOST.os, Windows) {
-            cmd_prefix = "LC_ALL=C"
-            cmd_suffix = "</dev/null >/dev/null"
-            null_file = /dev/null
-        } else {
+        cmd_suffix = "<$$QMAKE_NULL_DEVICE >$$QMAKE_NULL_DEVICE"
+        equals(QMAKE_HOST.os, Windows): \
             cmd_prefix = "set LC_ALL=C&"
-            cmd_suffix = "<NUL >NUL"
-            null_file = NUL
-        }
+        else: \
+            cmd_prefix = "LC_ALL=C"
 
         cxx_flags = $$QMAKE_CXXFLAGS
 
@@ -59,7 +55,7 @@ isEmpty($${target_prefix}.INCDIRS) {
 
         rim_qcc: \
             # Need the cc1plus and ld command lines to pick up the paths
-            cxx_flags += $$QMAKE_LFLAGS_SHLIB -o $$null_file -v
+            cxx_flags += $$QMAKE_LFLAGS_SHLIB -o $$QMAKE_NULL_DEVICE -v
         else: darwin:clang: \
             # Need to link to pick up library paths
             cxx_flags += $$QMAKE_LFLAGS_SHLIB -o /dev/null -v -Wl,-v
@@ -175,9 +171,7 @@ defineReplace(qtVariablesFromMSVC) {
 }
 
 defineReplace(qtVariablesFromGCC) {
-    null_device = /dev/null
-    equals(QMAKE_HOST.os, Windows): null_device = NUL
-    ret = $$system("$$1 -E $$system_quote($$PWD/data/macros.cpp) <$$null_device 2>$$null_device", lines, ec)
+    ret = $$system("$$1 -E $$system_quote($$PWD/data/macros.cpp) <$$QMAKE_NULL_DEVICE 2>$$QMAKE_NULL_DEVICE", lines, ec)
     !equals(ec, 0): qtCompilerErrror($$1)
     return($$ret)
 }
diff --git a/qmake/generators/win32/mingw_make.cpp b/qmake/generators/win32/mingw_make.cpp
index bad53dc5b7..2d69f708fb 100644
--- a/qmake/generators/win32/mingw_make.cpp
+++ b/qmake/generators/win32/mingw_make.cpp
@@ -36,12 +36,6 @@
 #include <stdlib.h>
 #include <time.h>
 
-#ifdef Q_OS_WIN
-#define NULL_DEVICE "NUL"
-#else
-#define NULL_DEVICE "/dev/null"
-#endif
-
 QT_BEGIN_NAMESPACE
 
 MingwMakefileGenerator::MingwMakefileGenerator() : Win32MakefileGenerator()
@@ -329,7 +323,7 @@ void MingwMakefileGenerator::writeBuildRulesPart(QTextStream &t)
     if(!project->isEmpty("QMAKE_PRE_LINK"))
         t << "\n\t" <<var("QMAKE_PRE_LINK");
     if(project->isActiveConfig("staticlib") && project->first("TEMPLATE") == "lib") {
-        t << "\n\t-$(DEL_FILE) $(DESTDIR_TARGET) 2>" NULL_DEVICE;
+        t << "\n\t-$(DEL_FILE) $(DESTDIR_TARGET) 2>$$QMAKE_NULL_DEVICE";
         if (project->values("OBJECTS").count() < var("QMAKE_LINK_OBJECT_MAX").toInt()) {
             t << "\n\t$(LIB) $(DESTDIR_TARGET) " << objectsLinkLine << " " ;
         } else {