diff --git a/py/hexagram/svg.py b/py/hexagram/svg.py
index 612f6a7..71609ae 100644
--- a/py/hexagram/svg.py
+++ b/py/hexagram/svg.py
@@ -26,7 +26,7 @@ def render_to_surface(path: str, surface: cairo.Surface, width: float, height: f
     surface
 
 def render_to_image(path: str, width: float, height: float, style: Optional[str]=None) -> cairo.Surface:
-    surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
+    surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, int(width), int(height))
 
     render_to_surface(path, surface, width, height, style)