--- a/gfx/thebes/src/gfxContext.cpp
+++ b/gfx/thebes/src/gfxContext.cpp
@@ -507,17 +507,17 @@ gfxFloat
 gfxContext::CurrentLineWidth() const
 {
     return cairo_get_line_width(mCairo);
 }
 
 void
 gfxContext::SetOperator(GraphicsOperator op)
 {
-    if (mFlags && FLAG_SIMPLIFY_OPERATORS) {
+    if (mFlags & FLAG_SIMPLIFY_OPERATORS) {
         if (op != OPERATOR_SOURCE &&
             op != OPERATOR_CLEAR &&
             op != OPERATOR_OVER)
             op = OPERATOR_OVER;
     }
 
     cairo_set_operator(mCairo, (cairo_operator_t)op);
 }