diff --git a/src/alire/alire-roots-editable.adb b/src/alire/alire-roots-editable.adb
index 81c11b4d0..a5749f5fb 100644
--- a/src/alire/alire-roots-editable.adb
+++ b/src/alire/alire-roots-editable.adb
@@ -1,6 +1,7 @@
 with Alire.Conditional;
 with Alire.Dependencies.Diffs;
 with Alire.Directories;
+with Alire.Index;
 with Alire.Manifest;
 with Alire.Origins;
 with Alire.Roots.Optional;
@@ -78,8 +79,9 @@ package body Alire.Roots.Editable is
    -- Add_Dependency --
    --------------------
 
-   procedure Add_Dependency (This : in out Root;
-                             Dep  : Dependencies.Dependency)
+   procedure Add_Dependency (This          : in out Root;
+                             Dep           : Dependencies.Dependency;
+                             Allow_Unknown : Boolean := Alire.Force)
    is
 
       --------------------
@@ -125,6 +127,14 @@ package body Alire.Roots.Editable is
 
    begin
 
+      --  Reject if unknown
+
+      if not Allow_Unknown and then not Index.Exists (Dep.Crate) then
+         Alire.Recoverable_Error
+           ("Cannot add crate '" & Alire.Utils.TTY.Name (Dep.Crate)
+            & "' not found in index.");
+      end if;
+
       --  Do not add if already a direct dependency
 
       if Release (This.Edit).Depends_On (Dep.Crate, This.Edit.Environment) then
@@ -287,7 +297,9 @@ package body Alire.Roots.Editable is
                  (Crate,
                   (if Pin_Root.Is_Valid and then not Pin_Is_Parent_Crate
                    then Pin_Root.Updatable_Dependency.Versions
-                   else Semver.Extended.Any)));
+                   else Semver.Extended.Any)),
+               Allow_Unknown => True);
+            --  Pins to local paths are more likely not to be indexed
          end if;
 
          --  Remove any previous pin for this crate
diff --git a/src/alire/alire-roots-editable.ads b/src/alire/alire-roots-editable.ads
index cf1b45e53..8fea2cfb1 100644
--- a/src/alire/alire-roots-editable.ads
+++ b/src/alire/alire-roots-editable.ads
@@ -53,10 +53,11 @@ package Alire.Roots.Editable is
    --  created, we need to reload the manifest. The solution remains
    --  untouched (use Update to recompute a fresh solution).
 
-   procedure Add_Dependency (This : in out Root;
-                             Dep  : Dependencies.Dependency);
+   procedure Add_Dependency (This          : in out Root;
+                             Dep           : Dependencies.Dependency;
+                             Allow_Unknown : Boolean := Alire.Force);
    --  Add a dependency, or raise Checked_Error is Dep is already among direct
-   --  dependencies.
+   --  dependencies. Recoverable error if Dep is unknown, unless Allow_Unknown.
 
    procedure Remove_Dependency (This  : in out Root;
                                 Crate : Crate_Name;
diff --git a/testsuite/tests/with/changes-info/test.py b/testsuite/tests/with/changes-info/test.py
index fc5514387..ad6bc8b15 100644
--- a/testsuite/tests/with/changes-info/test.py
+++ b/testsuite/tests/with/changes-info/test.py
@@ -27,8 +27,8 @@
              p.out, flags=re.S)
 
 ###############################################################################
-# Check adding a missing crate
-p = run_alr('with', 'unobtanium', quiet=False)
+# Check adding a missing crate (with forcing)
+p = run_alr('with', 'unobtanium', quiet=False, force=True)
 assert_match(".*" +
              re.escape("""Requested changes:
 
@@ -40,6 +40,14 @@
    +! unobtanium * (new,missing:unknown)""") + ".*",
              p.out, flags=re.S)
 
+# Remove the missing crate for following tests
+run_alr("with", "--del", "unobtanium")
+
+# Check adding without forcing for simpler error message
+p = run_alr('with', 'unobtanium', force=False, complain_on_error=False)
+assert_match(".*Cannot add crate 'unobtanium' not found in index",
+             p.out)
+
 ###############################################################################
 # Check adding a pinned dir (the dir must exist)
 os.mkdir("local_crate")