diff --git a/src/Lean/Attributes.lean b/src/Lean/Attributes.lean
index 26d36b60df..fb25418d10 100644
--- a/src/Lean/Attributes.lean
+++ b/src/Lean/Attributes.lean
@@ -47,137 +47,9 @@ builtin_initialize attributeMapRef : IO.Ref (PersistentHashMap Name AttributeImp
 def registerBuiltinAttribute (attr : AttributeImpl) : IO Unit := do
   let m ← attributeMapRef.get
   if m.contains attr.name then throw (IO.userError ("invalid builtin attribute declaration, '" ++ toString attr.name ++ "' has already been used"))
-  unless (← IO.initializing) do throw (IO.userError "failed to register attribute, attributes can only be registered during initialization")
+  unless (← IO.initializing) || (← importing) do throw (IO.userError "failed to register attribute, attributes can only be registered during initialization")
   attributeMapRef.modify fun m => m.insert attr.name attr
 
-abbrev AttributeImplBuilder := List DataValue → Except String AttributeImpl
-abbrev AttributeImplBuilderTable := Std.HashMap Name AttributeImplBuilder
-
-builtin_initialize attributeImplBuilderTableRef : IO.Ref AttributeImplBuilderTable ← IO.mkRef {}
-
-def registerAttributeImplBuilder (builderId : Name) (builder : AttributeImplBuilder) : IO Unit := do
-  let table ← attributeImplBuilderTableRef.get
-  if table.contains builderId then throw (IO.userError ("attribute implementation builder '" ++ toString builderId ++ "' has already been declared"))
-  attributeImplBuilderTableRef.modify fun table => table.insert builderId builder
-
-def mkAttributeImplOfBuilder (builderId : Name) (args : List DataValue) : IO AttributeImpl := do
-  let table ← attributeImplBuilderTableRef.get
-  match table.find? builderId with
-  | none         => throw (IO.userError ("unknown attribute implementation builder '" ++ toString builderId ++ "'"))
-  | some builder => IO.ofExcept $ builder args
-
-inductive AttributeExtensionOLeanEntry where
-  | decl (declName : Name) -- `declName` has type `AttributeImpl`
-  | builder (builderId : Name) (args : List DataValue)
-
-structure AttributeExtensionState where
-  newEntries : List AttributeExtensionOLeanEntry := []
-  map        : PersistentHashMap Name AttributeImpl
-  deriving Inhabited
-
-abbrev AttributeExtension := PersistentEnvExtension AttributeExtensionOLeanEntry (AttributeExtensionOLeanEntry × AttributeImpl) AttributeExtensionState
-
-private def AttributeExtension.mkInitial : IO AttributeExtensionState := do
-  let map ← attributeMapRef.get
-  pure { map := map }
-
-unsafe def mkAttributeImplOfConstantUnsafe (env : Environment) (opts : Options) (declName : Name) : Except String AttributeImpl :=
-  match env.find? declName with
-  | none      => throw ("unknow constant '" ++ toString declName ++ "'")
-  | some info =>
-    match info.type with
-    | Expr.const `Lean.AttributeImpl _ _ => env.evalConst AttributeImpl opts declName
-    | _ => throw ("unexpected attribute implementation type at '" ++ toString declName ++ "' (`AttributeImpl` expected")
-
-@[implementedBy mkAttributeImplOfConstantUnsafe]
-constant mkAttributeImplOfConstant (env : Environment) (opts : Options) (declName : Name) : Except String AttributeImpl
-
-def mkAttributeImplOfEntry (env : Environment) (opts : Options) (e : AttributeExtensionOLeanEntry) : IO AttributeImpl :=
-  match e with
-  | AttributeExtensionOLeanEntry.decl declName          => IO.ofExcept $ mkAttributeImplOfConstant env opts declName
-  | AttributeExtensionOLeanEntry.builder builderId args => mkAttributeImplOfBuilder builderId args
-
-private def AttributeExtension.addImported (es : Array (Array AttributeExtensionOLeanEntry)) : ImportM AttributeExtensionState := do
-  let ctx ← read
-  let map ← attributeMapRef.get
-  let map ← es.foldlM
-    (fun map entries =>
-      entries.foldlM
-        (fun (map : PersistentHashMap Name AttributeImpl) entry => do
-          let attrImpl ← liftM $ mkAttributeImplOfEntry ctx.env ctx.opts entry
-          pure $ map.insert attrImpl.name attrImpl)
-        map)
-    map
-  pure { map := map }
-
-private def addAttrEntry (s : AttributeExtensionState) (e : AttributeExtensionOLeanEntry × AttributeImpl) : AttributeExtensionState :=
-  { s with map := s.map.insert e.2.name e.2, newEntries := e.1 :: s.newEntries }
-
-builtin_initialize attributeExtension : AttributeExtension ←
-  registerPersistentEnvExtension {
-    name            := `attrExt,
-    mkInitial       := AttributeExtension.mkInitial,
-    addImportedFn   := AttributeExtension.addImported,
-    addEntryFn      := addAttrEntry,
-    exportEntriesFn := fun s => s.newEntries.reverse.toArray,
-    statsFn         := fun s => format "number of local entries: " ++ format s.newEntries.length
-  }
-
-/- Return true iff `n` is the name of a registered attribute. -/
-@[export lean_is_attribute]
-def isBuiltinAttribute (n : Name) : IO Bool := do
-  let m ← attributeMapRef.get; pure (m.contains n)
-
-/- Return the name of all registered attributes. -/
-def getBuiltinAttributeNames : IO (List Name) := do
-  let m ← attributeMapRef.get; pure $ m.foldl (fun r n _ => n::r) []
-
-def getBuiltinAttributeImpl (attrName : Name) : IO AttributeImpl := do
-  let m ← attributeMapRef.get
-  match m.find? attrName with
-  | some attr => pure attr
-  | none      => throw (IO.userError ("unknown attribute '" ++ toString attrName ++ "'"))
-
-@[export lean_attribute_application_time]
-def getBuiltinAttributeApplicationTime (n : Name) : IO AttributeApplicationTime := do
-  let attr ← getBuiltinAttributeImpl n
-  pure attr.applicationTime
-
-def isAttribute (env : Environment) (attrName : Name) : Bool :=
-  (attributeExtension.getState env).map.contains attrName
-
-def getAttributeNames (env : Environment) : List Name :=
-  let m := (attributeExtension.getState env).map
-  m.foldl (fun r n _ => n::r) []
-
-def getAttributeImpl (env : Environment) (attrName : Name) : Except String AttributeImpl :=
-  let m := (attributeExtension.getState env).map
-  match m.find? attrName with
-  | some attr => pure attr
-  | none      => throw ("unknown attribute '" ++ toString attrName ++ "'")
-
-def registerAttributeOfDecl (env : Environment) (opts : Options) (attrDeclName : Name) : Except String Environment := do
-  let attrImpl ← mkAttributeImplOfConstant env opts attrDeclName
-  if isAttribute env attrImpl.name then
-    throw ("invalid builtin attribute declaration, '" ++ toString attrImpl.name ++ "' has already been used")
-  else
-    pure $ attributeExtension.addEntry env (AttributeExtensionOLeanEntry.decl attrDeclName, attrImpl)
-
-def registerAttributeOfBuilder (env : Environment) (builderId : Name) (args : List DataValue) : IO Environment := do
-  let attrImpl ← mkAttributeImplOfBuilder builderId args
-  if isAttribute env attrImpl.name then
-    throw (IO.userError ("invalid builtin attribute declaration, '" ++ toString attrImpl.name ++ "' has already been used"))
-  else
-    pure $ attributeExtension.addEntry env (AttributeExtensionOLeanEntry.builder builderId args, attrImpl)
-
-def Attribute.add (declName : Name) (attrName : Name) (stx : Syntax) (kind := AttributeKind.global) : AttrM Unit := do
-  let attr ← ofExcept <| getAttributeImpl (← getEnv) attrName
-  attr.add declName stx kind
-
-def Attribute.erase (declName : Name) (attrName : Name) : AttrM Unit := do
-  let attr ← ofExcept <| getAttributeImpl (← getEnv) attrName
-  attr.erase declName
-
 /-
   Helper methods for decoding the parameters of builtin attributes that are defined before `Lean.Parser`.
   We have the following ones:
@@ -406,4 +278,148 @@ def setValue {α : Type} (attrs : EnumAttributes α) (env : Environment) (decl :
 
 end EnumAttributes
 
+/-
+  Attribute extension and builders. We use builders to implement attribute factories for parser categories.
+-/
+
+abbrev AttributeImplBuilder := List DataValue → Except String AttributeImpl
+abbrev AttributeImplBuilderTable := Std.HashMap Name AttributeImplBuilder
+
+builtin_initialize attributeImplBuilderTableRef : IO.Ref AttributeImplBuilderTable ← IO.mkRef {}
+
+def registerAttributeImplBuilder (builderId : Name) (builder : AttributeImplBuilder) : IO Unit := do
+  let table ← attributeImplBuilderTableRef.get
+  if table.contains builderId then throw (IO.userError ("attribute implementation builder '" ++ toString builderId ++ "' has already been declared"))
+  attributeImplBuilderTableRef.modify fun table => table.insert builderId builder
+
+def mkAttributeImplOfBuilder (builderId : Name) (args : List DataValue) : IO AttributeImpl := do
+  let table ← attributeImplBuilderTableRef.get
+  match table.find? builderId with
+  | none         => throw (IO.userError ("unknown attribute implementation builder '" ++ toString builderId ++ "'"))
+  | some builder => IO.ofExcept $ builder args
+
+inductive AttributeExtensionOLeanEntry where
+  | decl (declName : Name) -- `declName` has type `AttributeImpl`
+  | builder (builderId : Name) (args : List DataValue)
+
+structure AttributeExtensionState where
+  newEntries : List AttributeExtensionOLeanEntry := []
+  map        : PersistentHashMap Name AttributeImpl
+  deriving Inhabited
+
+abbrev AttributeExtension := PersistentEnvExtension AttributeExtensionOLeanEntry (AttributeExtensionOLeanEntry × AttributeImpl) AttributeExtensionState
+
+private def AttributeExtension.mkInitial : IO AttributeExtensionState := do
+  let map ← attributeMapRef.get
+  pure { map := map }
+
+unsafe def mkAttributeImplOfConstantUnsafe (env : Environment) (opts : Options) (declName : Name) : Except String AttributeImpl :=
+  match env.find? declName with
+  | none      => throw ("unknow constant '" ++ toString declName ++ "'")
+  | some info =>
+    match info.type with
+    | Expr.const `Lean.AttributeImpl _ _ => env.evalConst AttributeImpl opts declName
+    | _ => throw ("unexpected attribute implementation type at '" ++ toString declName ++ "' (`AttributeImpl` expected")
+
+@[implementedBy mkAttributeImplOfConstantUnsafe]
+constant mkAttributeImplOfConstant (env : Environment) (opts : Options) (declName : Name) : Except String AttributeImpl
+
+def mkAttributeImplOfEntry (env : Environment) (opts : Options) (e : AttributeExtensionOLeanEntry) : IO AttributeImpl :=
+  match e with
+  | AttributeExtensionOLeanEntry.decl declName          => IO.ofExcept $ mkAttributeImplOfConstant env opts declName
+  | AttributeExtensionOLeanEntry.builder builderId args => mkAttributeImplOfBuilder builderId args
+
+private def AttributeExtension.addImported (es : Array (Array AttributeExtensionOLeanEntry)) : ImportM AttributeExtensionState := do
+  let ctx ← read
+  let map ← attributeMapRef.get
+  let map ← es.foldlM
+    (fun map entries =>
+      entries.foldlM
+        (fun (map : PersistentHashMap Name AttributeImpl) entry => do
+          let attrImpl ← liftM $ mkAttributeImplOfEntry ctx.env ctx.opts entry
+          pure $ map.insert attrImpl.name attrImpl)
+        map)
+    map
+  pure { map := map }
+
+private def addAttrEntry (s : AttributeExtensionState) (e : AttributeExtensionOLeanEntry × AttributeImpl) : AttributeExtensionState :=
+  { s with map := s.map.insert e.2.name e.2, newEntries := e.1 :: s.newEntries }
+
+builtin_initialize attributeExtension : AttributeExtension ←
+  registerPersistentEnvExtension {
+    name            := `attrExt,
+    mkInitial       := AttributeExtension.mkInitial,
+    addImportedFn   := AttributeExtension.addImported,
+    addEntryFn      := addAttrEntry,
+    exportEntriesFn := fun s => s.newEntries.reverse.toArray,
+    statsFn         := fun s => format "number of local entries: " ++ format s.newEntries.length
+  }
+
+/- Return true iff `n` is the name of a registered attribute. -/
+@[export lean_is_attribute]
+def isBuiltinAttribute (n : Name) : IO Bool := do
+  let m ← attributeMapRef.get; pure (m.contains n)
+
+/- Return the name of all registered attributes. -/
+def getBuiltinAttributeNames : IO (List Name) := do
+  let m ← attributeMapRef.get; pure $ m.foldl (fun r n _ => n::r) []
+
+def getBuiltinAttributeImpl (attrName : Name) : IO AttributeImpl := do
+  let m ← attributeMapRef.get
+  match m.find? attrName with
+  | some attr => pure attr
+  | none      => throw (IO.userError ("unknown attribute '" ++ toString attrName ++ "'"))
+
+@[export lean_attribute_application_time]
+def getBuiltinAttributeApplicationTime (n : Name) : IO AttributeApplicationTime := do
+  let attr ← getBuiltinAttributeImpl n
+  pure attr.applicationTime
+
+def isAttribute (env : Environment) (attrName : Name) : Bool :=
+  (attributeExtension.getState env).map.contains attrName
+
+def getAttributeNames (env : Environment) : List Name :=
+  let m := (attributeExtension.getState env).map
+  m.foldl (fun r n _ => n::r) []
+
+def getAttributeImpl (env : Environment) (attrName : Name) : Except String AttributeImpl :=
+  let m := (attributeExtension.getState env).map
+  match m.find? attrName with
+  | some attr => pure attr
+  | none      => throw ("unknown attribute '" ++ toString attrName ++ "'")
+
+def registerAttributeOfDecl (env : Environment) (opts : Options) (attrDeclName : Name) : Except String Environment := do
+  let attrImpl ← mkAttributeImplOfConstant env opts attrDeclName
+  if isAttribute env attrImpl.name then
+    throw ("invalid builtin attribute declaration, '" ++ toString attrImpl.name ++ "' has already been used")
+  else
+    pure $ attributeExtension.addEntry env (AttributeExtensionOLeanEntry.decl attrDeclName, attrImpl)
+
+def registerAttributeOfBuilder (env : Environment) (builderId : Name) (args : List DataValue) : IO Environment := do
+  let attrImpl ← mkAttributeImplOfBuilder builderId args
+  if isAttribute env attrImpl.name then
+    throw (IO.userError ("invalid builtin attribute declaration, '" ++ toString attrImpl.name ++ "' has already been used"))
+  else
+    pure $ attributeExtension.addEntry env (AttributeExtensionOLeanEntry.builder builderId args, attrImpl)
+
+def Attribute.add (declName : Name) (attrName : Name) (stx : Syntax) (kind := AttributeKind.global) : AttrM Unit := do
+  let attr ← ofExcept <| getAttributeImpl (← getEnv) attrName
+  attr.add declName stx kind
+
+def Attribute.erase (declName : Name) (attrName : Name) : AttrM Unit := do
+  let attr ← ofExcept <| getAttributeImpl (← getEnv) attrName
+  attr.erase declName
+
+builtin_initialize
+  -- See comment at `updateEnvAttributesRef`
+  updateEnvAttributesRef.set fun env => do
+    let map ← attributeMapRef.get
+    let s ← attributeExtension.getState env
+    let s := map.foldl (init := s) fun s attrName attrImpl =>
+      if s.map.contains attrName then
+        s
+      else
+        { s with map := s.map.insert attrName attrImpl }
+    return attributeExtension.setState env s
+
 end Lean
diff --git a/src/Lean/Compiler/InitAttr.lean b/src/Lean/Compiler/InitAttr.lean
index b292abb6c8..30b4272f8c 100644
--- a/src/Lean/Compiler/InitAttr.lean
+++ b/src/Lean/Compiler/InitAttr.lean
@@ -49,8 +49,9 @@ unsafe def registerInitAttrUnsafe (attrName : Name) (runAfterImport : Bool) : IO
         for modEntries in entries do
           for (decl, initDecl) in modEntries do
             if initDecl.isAnonymous then
-              _ ← IO.ofExcept $ ctx.env.evalConst (IO Unit) ctx.opts decl
-            else runInit ctx.env ctx.opts decl initDecl
+              discard <| IO.ofExcept $ ctx.env.evalConst (IO Unit) ctx.opts decl
+            else
+              runInit ctx.env ctx.opts decl initDecl
   }
 
 @[implementedBy registerInitAttrUnsafe]
diff --git a/src/Lean/Environment.lean b/src/Lean/Environment.lean
index dc96222dc5..193ab5d8cd 100644
--- a/src/Lean/Environment.lean
+++ b/src/Lean/Environment.lean
@@ -570,6 +570,17 @@ private def setImportedEntries (env : Environment) (mods : Array ModuleData) (st
       env ← extDescr.toEnvExtension.modifyState env fun s => { s with importedEntries := s.importedEntries.push entries }
   return env
 
+/-
+  "Forward declaration" needed for updating the attribute table with user-defined attributes.
+  User-defined attributes are declared using the `initialize` command. The `initialize` command is just syntax sugar for the `init` attribute.
+  The `init` attribute is initialized after the `attributeExtension` is initialized. We cannot change the order since the `init` attribute is an attribute,
+  and requires this extension.
+  The `attributeExtension` initializer uses `attributeMapRef` to initialize the attribute mapping.
+  When we a new user-defined attribute declaration is imported, `attributeMapRef` is updated.
+  Later, we set this method with code that adds the user-defined attributes that were imported after we initialized `attributeExtension`.
+-/
+builtin_initialize updateEnvAttributesRef : IO.Ref (Environment → IO Environment) ← IO.mkRef (fun env => pure env)
+
 private partial def finalizePersistentExtensions (env : Environment) (mods : Array ModuleData) (opts : Options) : IO Environment := do
   loop 0 env
 where
@@ -588,6 +599,8 @@ where
         -- a user-defined persistent extension is imported.
         -- Thus, we invoke `setImportedEntries` to update the array `importedEntries` with the entries for the new extensions.
         env ← setImportedEntries env mods prevSize
+        -- See comment at `updateEnvAttributesRef`
+        env ← (← updateEnvAttributesRef.get) env
       loop (i + 1) env
     else
       return env
diff --git a/src/shell/CMakeLists.txt b/src/shell/CMakeLists.txt
index 4949a8729a..b3bdb5718a 100644
--- a/src/shell/CMakeLists.txt
+++ b/src/shell/CMakeLists.txt
@@ -187,3 +187,11 @@ add_test(NAME leanpkgtest_user_ext
            export PATH=${LEAN_BIN}:$PATH
            find . -name '*.olean' -delete
            leanpkg build | grep 'world, hello, test'")
+
+add_test(NAME leanpkgtest_user_attr
+         WORKING_DIRECTORY "${LEAN_SOURCE_DIR}/../tests/leanpkg/user_attr"
+         COMMAND bash -c "
+           set -eu
+           export PATH=${LEAN_BIN}:$PATH
+           find . -name '*.olean' -delete
+           leanpkg build")
diff --git a/tests/leanpkg/user_attr/.gitignore b/tests/leanpkg/user_attr/.gitignore
new file mode 100644
index 0000000000..796b96d1c4
--- /dev/null
+++ b/tests/leanpkg/user_attr/.gitignore
@@ -0,0 +1 @@
+/build
diff --git a/tests/leanpkg/user_attr/UserAttr.lean b/tests/leanpkg/user_attr/UserAttr.lean
new file mode 100644
index 0000000000..ec633fea1c
--- /dev/null
+++ b/tests/leanpkg/user_attr/UserAttr.lean
@@ -0,0 +1,12 @@
+import UserAttr.Tst
+
+open Lean
+
+def tst : MetaM Unit := do
+  let env ← getEnv
+  assert! (blaAttr.hasTag env `f)
+  assert! (blaAttr.hasTag env `g)
+  assert! !(blaAttr.hasTag env `id)
+  pure ()
+
+#eval tst
diff --git a/tests/leanpkg/user_attr/UserAttr/BlaAttr.lean b/tests/leanpkg/user_attr/UserAttr/BlaAttr.lean
new file mode 100644
index 0000000000..7314fc152b
--- /dev/null
+++ b/tests/leanpkg/user_attr/UserAttr/BlaAttr.lean
@@ -0,0 +1,5 @@
+import Lean
+
+open Lean
+
+initialize blaAttr : TagAttribute ← registerTagAttribute `bla "simple user defined attribute"
diff --git a/tests/leanpkg/user_attr/UserAttr/Tst.lean b/tests/leanpkg/user_attr/UserAttr/Tst.lean
new file mode 100644
index 0000000000..f80db320f8
--- /dev/null
+++ b/tests/leanpkg/user_attr/UserAttr/Tst.lean
@@ -0,0 +1,4 @@
+import UserAttr.BlaAttr
+
+@[bla] def f (x : Nat) := x + 2
+@[bla] def g (x : Nat) := x + 1
diff --git a/tests/leanpkg/user_attr/leanpkg.toml b/tests/leanpkg/user_attr/leanpkg.toml
new file mode 100644
index 0000000000..155f689776
--- /dev/null
+++ b/tests/leanpkg/user_attr/leanpkg.toml
@@ -0,0 +1,3 @@
+[package]
+name = "UserAttr"
+version = "0.1"