diff --git a/src/frontends/qt/GuiBox.cpp b/src/frontends/qt/GuiBox.cpp
index 298009da1b..0d22aa7963 100644
--- a/src/frontends/qt/GuiBox.cpp
+++ b/src/frontends/qt/GuiBox.cpp
@@ -32,10 +32,6 @@
 #include <QLineEdit>
 #include <QPushButton>
 
-#ifdef IN
-#undef IN
-#endif
-
 using namespace std;
 
 
diff --git a/src/frontends/qt/GuiDocument.cpp b/src/frontends/qt/GuiDocument.cpp
index 7e1ec248b1..0244bfdfe8 100644
--- a/src/frontends/qt/GuiDocument.cpp
+++ b/src/frontends/qt/GuiDocument.cpp
@@ -85,10 +85,6 @@
 #include <sstream>
 #include <vector>
 
-#ifdef IN
-#undef IN
-#endif
-
 
 // a style sheet for buttons
 // this is for example used for the background color setting button
diff --git a/src/support/os_win32.h b/src/support/os_win32.h
index 3f278c3bd0..a656f6f182 100644
--- a/src/support/os_win32.h
+++ b/src/support/os_win32.h
@@ -49,6 +49,9 @@
 #include <tchar.h>
 #include <psapi.h>
 
+#ifdef IN
+#undef IN // used in Length::UNIT enum
+#endif
 
 namespace lyx {
 namespace support {