diff --git a/mkspecs/dilos-g++/qplatformdefs.h b/mkspecs/dilos-g++/qplatformdefs.h
index f1c2a3d0..b8d57efa 100644
--- a/mkspecs/dilos-g++/qplatformdefs.h
+++ b/mkspecs/dilos-g++/qplatformdefs.h
@@ -112,5 +112,6 @@ extern "C" int gethostname(char *, int);
 #define QT_VSNPRINTF		::vsnprintf
 #endif
 
+#define QT_MITSHM
 
 #endif // TQPLATFORMDEFS_H
diff --git a/mkspecs/freebsd-clang/qplatformdefs.h b/mkspecs/freebsd-clang/qplatformdefs.h
index cef0a5e2..1841a9c9 100644
--- a/mkspecs/freebsd-clang/qplatformdefs.h
+++ b/mkspecs/freebsd-clang/qplatformdefs.h
@@ -99,5 +99,6 @@
 #define QT_AOUT_UNDERSCORE
 #endif
 
+#define QT_MITSHM
 
 #endif // TQPLATFORMDEFS_H
diff --git a/mkspecs/linux-g++-32/qplatformdefs.h b/mkspecs/linux-g++-32/qplatformdefs.h
index e6dc1fcb..68530060 100644
--- a/mkspecs/linux-g++-32/qplatformdefs.h
+++ b/mkspecs/linux-g++-32/qplatformdefs.h
@@ -77,5 +77,6 @@
 #define QT_VSNPRINTF		::vsnprintf
 #endif
 
+#define QT_MITSHM
 
 #endif // TQPLATFORMDEFS_H
diff --git a/mkspecs/linux-g++-64/qplatformdefs.h b/mkspecs/linux-g++-64/qplatformdefs.h
index 951a476f..fd100489 100644
--- a/mkspecs/linux-g++-64/qplatformdefs.h
+++ b/mkspecs/linux-g++-64/qplatformdefs.h
@@ -84,5 +84,6 @@
 #define QT_VSNPRINTF		::vsnprintf
 #endif
 
+#define QT_MITSHM
 
 #endif // TQPLATFORMDEFS_H