Shadergraph: Sample Cubemap seems to not decode HDR color

Hi! I'm creating a shadergraph that shows a portion of an image skybox, but the colors are not correct.

I'm using an HDR image file, which appears to be encoded in RGBM format. Using the Sample Cubemap node produces strange results. The hue of the pixels is right, but they look overly saturated and the brightness has no dynamic range. I assume this is the RGBM encoded pixels being shown directly.

What's happening? Does the cubemap node not Work with HDR images? Do I need to decode the RGBM values manually? Multiplying the RGB values by the alpha looks like it goes in the right direction, but it is essential that it looks exactly right, 100%.

Update: Saving the same image as PNG after tonemapping manually made the colors look correct. Maybe the Sample Cubemap node does not support RGBM files?