diff --git a/repo2docker/utils.py b/repo2docker/utils.py
index 443db97e..9c2769e1 100644
--- a/repo2docker/utils.py
+++ b/repo2docker/utils.py
@@ -543,4 +543,5 @@ def get_platform():
         # OSX reports arm64
         return "linux/arm64"
     else:
-        raise ValueError("Unsupported platform {m}")
+        warnings.warn(f"Unexpected platform '{m}', defaulting to linux/amd64")
+        return "linux/amd64"