diff --git a/src/frontend/wdisp/windisp.c b/src/frontend/wdisp/windisp.c
index 24a092aa1..00cc0bea0 100644
--- a/src/frontend/wdisp/windisp.c
+++ b/src/frontend/wdisp/windisp.c
@@ -12,6 +12,16 @@
 #include "graph.h"
 #include "ftedev.h"
 #include "ftedbgra.h"
+
+/*
+ * The ngspice.h file included above defines BOOLEAN (via bool.h) and this
+ * clashes with the definition obtained from windows.h (via winnt.h).
+ * However, BOOLEAN is not used by this file so we can work round this problem
+ * by undefining BOOLEAN before including windows.h
+ * SJB - May 2005
+ */
+#undef BOOLEAN
+
 #pragma warn -dup 		// wegen Redefinition von NUMCOLORS
 #include <windows.h>
 #include <windowsx.h>
diff --git a/src/frontend/wdisp/winprint.c b/src/frontend/wdisp/winprint.c
index e7b751c29..7c09de9f2 100644
--- a/src/frontend/wdisp/winprint.c
+++ b/src/frontend/wdisp/winprint.c
@@ -12,6 +12,16 @@
 #include "graph.h"
 #include "ftedev.h"
 #include "ftedbgra.h"
+
+/*
+ * The ngspice.h file included above defines BOOLEAN (via bool.h) and this
+ * clashes with the definition obtained from windows.h (via winnt.h).
+ * However, BOOLEAN is not used by this file so we can work round this problem
+ * by undefining BOOLEAN before including windows.h
+ * SJB - May 2005
+ */
+#undef BOOLEAN
+
 #pragma warn -dup
 #include <windows.h>
 #include <windowsx.h>