diff --git a/src/borg/helpers/parseformat.py b/src/borg/helpers/parseformat.py
index bb38092d0..fd8ffbe52 100644
--- a/src/borg/helpers/parseformat.py
+++ b/src/borg/helpers/parseformat.py
@@ -616,6 +616,19 @@ class Location:
 
         self.raw = text  # as given by user, might contain placeholders
         self.processed = replace_placeholders(self.raw, overrides)  # after placeholder replacement
+        if "::" in self.processed:
+            repo, archive = self.processed.split("::", 1)
+            raise ValueError(
+                f'Invalid location format: "{self.processed}". '
+                "Borg 2 does not accept repo::archive syntax. "
+                "Corrected command lines:\n"
+                f"borg -r {repo} list {archive}\n"
+                f"export BORG_REPO={repo}\n"
+                f"borg list {archive}\n"
+                f"borg -r {repo} repo-info\n"
+                f"export BORG_REPO={repo}\n"
+                f"borg repo-info"
+            )
         valid = self._parse(self.processed)
         if valid:
             self.valid = True