diff --git a/pkgs/by-name/gi/gildas/update.py b/pkgs/by-name/gi/gildas/update.py
index 19e0d09294b1..7f832232326e 100755
--- a/pkgs/by-name/gi/gildas/update.py
+++ b/pkgs/by-name/gi/gildas/update.py
@@ -85,11 +85,14 @@ def get_hash(srcVersion):
     """
 
     url = f"http://www.iram.fr/~gildas/dist/gildas-src-{srcVersion}.tar.xz"
-    srcHash = (
-        subprocess.check_output(["nix-prefetch-url", url, "--unpack"]).decode().strip()
+    srcHash = subprocess.check_output(["nix-prefetch-url", url]).decode().strip()
+    # Convert to SRI representation
+    srcSRIHash = (
+        subprocess.check_output(["nix-hash", "--to-sri", "--type", "sha256", srcHash])
+        .decode()
+        .strip()
     )
-
-    return f"sha256:{srcHash}"
+    return srcSRIHash
 
 
 def get_package_attribute(attr):