Index: win32ss/gdi/ntgdi/pen.c
===================================================================
--- win32ss/gdi/ntgdi/pen.c	(revision 75919)
+++ win32ss/gdi/ntgdi/pen.c	(working copy)
@@ -93,6 +93,32 @@
     static ULONG aulStyleDashDotDot[] = { 3, 1, 1, 1, 1, 1 };
     ULONG i;
 
+    /* check styles */
+    switch (dwPenStyle & PS_ENDCAP_MASK)
+    {
+        case PS_ENDCAP_ROUND: case PS_ENDCAP_SQUARE: case PS_ENDCAP_FLAT:
+            break;
+        default:
+            EngSetLastError(ERROR_INVALID_PARAMETER);
+            return NULL;
+    }
+    switch (dwPenStyle & PS_JOIN_MASK)
+    {
+        case PS_JOIN_ROUND: case PS_JOIN_BEVEL: case PS_JOIN_MITER:
+            break;
+        default:
+            EngSetLastError(ERROR_INVALID_PARAMETER);
+            return NULL;
+    }
+    switch (dwPenStyle & PS_TYPE_MASK)
+    {
+        case PS_COSMETIC: case PS_GEOMETRIC:
+            break;
+        default:
+            EngSetLastError(ERROR_INVALID_PARAMETER);
+            return NULL;
+    }
+
     dwWidth = abs(dwWidth);
 
     if ( (dwPenStyle & PS_STYLE_MASK) == PS_NULL)