diff --git a/master_changes.md b/master_changes.md
index 3c2b50005b0..2e4b2391851 100644
--- a/master_changes.md
+++ b/master_changes.md
@@ -55,6 +55,7 @@ users)
 
 ## Repository
   * Fix `OPAMCURL` and `OPAMFETCH` handling [#5607 @rjbou - fix #5597]
+  * Silently mark packages requiring an unsupported version of opam as unavailable [#5665 @kit-ty-kate - fix #5631]
 
 ## Lock
 
diff --git a/src/format/opamFile.ml b/src/format/opamFile.ml
index 54701b9426d..ab9f5d569aa 100644
--- a/src/format/opamFile.ml
+++ b/src/format/opamFile.ml
@@ -136,7 +136,7 @@ module MakeIO (F : IO_Arg) = struct
     with
     | OpamSystem.File_not_found _ ->
       None
-    | e ->
+    | Pp.Bad_format _ as e ->
       OpamStd.Exn.fatal e;
       if OpamFormatConfig.(!r.strict) then
         (OpamConsole.error "%s"
@@ -166,7 +166,7 @@ module MakeIO (F : IO_Arg) = struct
 
   let read_from_f f input =
     try f input with
-    | (Pp.Bad_version _ | Pp.Bad_format _) as e->
+    | Pp.Bad_format _ as e ->
       if OpamFormatConfig.(!r.strict) then
         (OpamConsole.error "%s" (Pp.string_of_bad_format e);
          OpamConsole.error_and_exit `File_error "Strict mode: aborting")
diff --git a/src/state/opamFileTools.ml b/src/state/opamFileTools.ml
index df182e48893..6ad387b2b29 100644
--- a/src/state/opamFileTools.ml
+++ b/src/state/opamFileTools.ml
@@ -1192,6 +1192,10 @@ let read_opam dir =
       (OpamPp.string_of_bad_format (OpamPp.Bad_format (snd err)));
     None
   | None, None -> None
+  | exception (OpamPp.Bad_version _bf) ->
+    log "opam-version unsupported on %s. Add as dummy unavailable package."
+      (OpamFile.to_string opam_file);
+    Some (OpamFile.OPAM.with_available (FBool false) OpamFile.OPAM.empty)
 
 let read_repo_opam ~repo_name ~repo_root dir =
   let open OpamStd.Option.Op in
diff --git a/tests/reftests/repository.test b/tests/reftests/repository.test
index 64321a6638d..6b14a7b9ff7 100644
--- a/tests/reftests/repository.test
+++ b/tests/reftests/repository.test
@@ -605,14 +605,12 @@ some-field-that-do-not-exist: true
 
 <><> Updating package repositories ><><><><><><><><><><><><><><><><><><><><><><>
 [oper] synchronised from file://${BASEDIR}/OPER3
-[ERROR] In ${OPAMTMP}/oper/packages/bad-opam-version/bad-opam-version.1/opam:
-        unsupported or missing file format version; should be 2.0 or older
-[ERROR] Strict mode: aborting
-[ERROR] Could not update repository "oper": OpamStd.OpamSys.Exit(30)
+opam-file                       opam-version unsupported on ${OPAMTMP}/oper/packages/bad-opam-version/bad-opam-version.1/opam. Add as dummy unavailable package.
 [repo] no changes from file://${BASEDIR}/REPO
 [repo2] no changes from file://${BASEDIR}/REPO2
-# Return code 40 #
+Now run 'opam upgrade' to apply any package updates.
 ### opam list -A --all-versions -s
+bad-opam-version.1
 foo.1
 foo.2
 foo.3
@@ -630,14 +628,15 @@ opam-version: "2.0"
 
 <><> Updating package repositories ><><><><><><><><><><><><><><><><><><><><><><>
 [oper] synchronised from file://${BASEDIR}/OPER3
-[ERROR] Could not update repository "oper": In ${OPAMTMP}/oper/packages/bad-opam-version/bad-opam-version.1/opam:
-        unsupported or missing file format version; should be 2.0 or older
+opam-file                       opam-version unsupported on ${OPAMTMP}/oper/packages/bad-opam-version/bad-opam-version.1/opam. Add as dummy unavailable package.
 [repo] synchronised from file://${BASEDIR}/REPO
-[ERROR] Could not update repository "repo": In ${OPAMTMP}/repo/packages/bad-opam-version/bad-opam-version.2/opam:
-        unsupported or missing file format version; should be 2.0 or older
+opam-file                       opam-version unsupported on ${OPAMTMP}/repo/packages/bad-opam-version/bad-opam-version.2/opam. Add as dummy unavailable package.
 [repo2] no changes from file://${BASEDIR}/REPO2
-# Return code 40 #
+Now run 'opam upgrade' to apply any package updates.
 ### opam list -A --all-versions -s
+a.1
+bad-opam-version.1
+bad-opam-version.2
 foo.1
 foo.2
 foo.3
@@ -650,14 +649,16 @@ third.3
 ### opam list -A --all-versions -s
 ### opam repository --this-switch add repo ./REPO
 [repo] Initialised
-[ERROR] Could not update repository "repo": In ${BASEDIR}/OPAM/repo/repo/packages/bad-opam-version/bad-opam-version.2/opam:
-        unsupported or missing file format version; should be 2.0 or older
-[ERROR] Initial repository fetch failed
-# Return code 40 #
 ### opam repository --this-switch add oper ./OPER3
 [oper] Initialised
-[ERROR] Could not update repository "oper": In ${BASEDIR}/OPAM/repo/oper/packages/bad-opam-version/bad-opam-version.1/opam:
-        unsupported or missing file format version; should be 2.0 or older
-[ERROR] Initial repository fetch failed
-# Return code 40 #
 ### opam list -A --all-versions -s
+a.1
+bad-opam-version.1
+bad-opam-version.2
+foo.1
+foo.2
+foo.3
+foo.4
+foo.5
+foo.6
+third.3