diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -1982,9 +1982,9 @@ def add(ui, repo, match, dryrun, listsub
     abort, warn = scmutil.checkportabilityalert(ui)
     if abort or warn:
         cca = scmutil.casecollisionauditor(ui, abort, repo.dirstate)
-    for f in repo.walk(match):
+    for f in wctx.walk(match):
         exact = match.exact(f)
-        if exact or not explicitonly and f not in repo.dirstate:
+        if exact or not explicitonly and f not in wctx:
             if cca:
                 cca(f)
             names.append(f)
diff --git a/tests/test-add.t b/tests/test-add.t
--- a/tests/test-add.t
+++ b/tests/test-add.t
@@ -126,6 +126,19 @@ Issue683: peculiarity with hg revert of 
   M a
   ? a.orig
 
+Forgotten file can be added back (as either clean or modified)
+
+  $ hg forget b
+  $ hg add b
+  $ hg st -A b
+  C b
+  $ hg forget b
+  $ echo modified > b
+  $ hg add b
+  $ hg st -A b
+  M b
+  $ hg revert -qC b
+
   $ hg add c && echo "unexpected addition of missing file"
   c: * (glob)
   [1]