diff --git a/initcairo.c b/initcairo.c
index 807fce3..bab7b4f 100644
--- a/initcairo.c
+++ b/initcairo.c
@@ -12,6 +12,7 @@ static Bool alwaysTruePredicate(Display *display, XEvent *event, XPointer arg)
 	return true;
 }
 
+// this computes center, radius and scalefactor out of ctx->matrix
 void updateDimensions(DrawingContext *ctx)
 {
 	double det = ctx->matrix.xx * ctx->matrix.yy - ctx->matrix.xy * ctx->matrix.yx;
diff --git a/limit_set.c b/limit_set.c
index fe7d053..f3543fe 100644
--- a/limit_set.c
+++ b/limit_set.c
@@ -501,7 +501,8 @@ void print(DrawingContext *screen)
 	file.width = screen->width;
 	file.height = screen->width / sqrt(2.0);
 	file.matrix = screen->matrix;
-	file.matrix.y0 += (file.height - screen->height) / 2.0; // recenter vertically
+	file.matrix.y0 += ((double)file.height - (double)screen->height) / 2.0; // recenter vertically
+	updateDimensions(&file);
 
 	surface = cairo_pdf_surface_create(filename, (double)file.width, (double)file.height);
     file.cairo = cairo_create(surface);