diff --git a/pkg/_fe_analyzer_shared/lib/src/flow_analysis/flow_analysis.dart b/pkg/_fe_analyzer_shared/lib/src/flow_analysis/flow_analysis.dart
index 54370490442..9a0d773fb46 100644
--- a/pkg/_fe_analyzer_shared/lib/src/flow_analysis/flow_analysis.dart
+++ b/pkg/_fe_analyzer_shared/lib/src/flow_analysis/flow_analysis.dart
@@ -71,6 +71,7 @@ class AssignedVariables<Node extends Object, Variable extends Object> {
   void declare(Variable variable) {
     assert(!_isFinished);
     _stack.last._declared.add(variable);
+    _anywhere._declared.add(variable);
   }
 
   /// This method may be called during pre-traversal, to mark the end of a
@@ -1737,7 +1738,8 @@ class FlowModel<Variable extends Object, Type extends Object> {
     Map<Variable?, VariableModel<Variable, Type>>? newVariableInfo;
 
     for (Variable variable in writtenVariables) {
-      VariableModel<Variable, Type> info = infoFor(variable);
+      VariableModel<Variable, Type>? info = variableInfo[variable];
+      if (info == null) continue;
       VariableModel<Variable, Type> newInfo =
           info.discardPromotionsAndMarkNotUnassigned();
       if (!identical(info, newInfo)) {
@@ -1749,16 +1751,8 @@ class FlowModel<Variable extends Object, Type extends Object> {
 
     for (Variable variable in capturedVariables) {
       VariableModel<Variable, Type>? info = variableInfo[variable];
-      if (info == null) {
-        (newVariableInfo ??=
-            new Map<Variable?, VariableModel<Variable, Type>>.of(
-                variableInfo))[variable] = new VariableModel<Variable, Type>(
-            promotedTypes: null,
-            tested: const [],
-            assigned: false,
-            unassigned: false,
-            ssaNode: null);
-      } else if (!info.writeCaptured) {
+      if (info == null) continue;
+      if (!info.writeCaptured) {
         (newVariableInfo ??=
             new Map<Variable?, VariableModel<Variable, Type>>.of(
                 variableInfo))[variable] = info.writeCapture();
@@ -3487,6 +3481,15 @@ class _FlowAnalysisImpl<Node extends Object, Statement extends Node,
     if (!_assignedVariables._isFinished) {
       _assignedVariables.finish();
     }
+    AssignedVariablesNodeInfo<Variable> anywhere = _assignedVariables._anywhere;
+    Set<Variable> implicitlyDeclaredVars = {
+      ...anywhere._read,
+      ...anywhere._written
+    };
+    implicitlyDeclaredVars.removeAll(anywhere._declared);
+    for (Variable variable in implicitlyDeclaredVars) {
+      declare(variable, true);
+    }
   }
 
   @override
diff --git a/pkg/_fe_analyzer_shared/test/flow_analysis/assigned_variables/data/constructor.dart b/pkg/_fe_analyzer_shared/test/flow_analysis/assigned_variables/data/constructor.dart
index 20220737ab1..1b7e73194cf 100644
--- a/pkg/_fe_analyzer_shared/test/flow_analysis/assigned_variables/data/constructor.dart
+++ b/pkg/_fe_analyzer_shared/test/flow_analysis/assigned_variables/data/constructor.dart
@@ -12,3 +12,10 @@ class C {
 class D {
   const D(bool b) : assert(b);
 }
+
+class E {
+  final String a;
+  final String? b;
+
+  const E(this.a, {this.b});
+}
diff --git a/pkg/_fe_analyzer_shared/test/flow_analysis/assigned_variables/data/topLevelVariable.dart b/pkg/_fe_analyzer_shared/test/flow_analysis/assigned_variables/data/topLevelVariable.dart
index b2b8e7df5aa..40b86c3b16e 100644
--- a/pkg/_fe_analyzer_shared/test/flow_analysis/assigned_variables/data/topLevelVariable.dart
+++ b/pkg/_fe_analyzer_shared/test/flow_analysis/assigned_variables/data/topLevelVariable.dart
@@ -2,6 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-dynamic /*member: x:assigned={a}*/ x = /*declared={a, b}*/ (int a, int b) {
+dynamic /*member: x1:assigned={a}*/ x1 = /*declared={a, b}*/ (int a, int b) {
   a = 0;
 };
+
+/*member: x2:none*/
+final x2 = new List.filled(0, null);
diff --git a/pkg/_fe_analyzer_shared/test/flow_analysis/flow_analysis_test.dart b/pkg/_fe_analyzer_shared/test/flow_analysis/flow_analysis_test.dart
index e85803ae204..a3700cdecea 100644
--- a/pkg/_fe_analyzer_shared/test/flow_analysis/flow_analysis_test.dart
+++ b/pkg/_fe_analyzer_shared/test/flow_analysis/flow_analysis_test.dart
@@ -3197,6 +3197,25 @@ main() {
         x.expr.as_('int').stmt, checkNotPromoted(x),
       ]);
     });
+
+    test('issue 47991', () {
+      var h = Harness();
+      var b = Var('b', 'bool');
+      var i = Var('i', 'int', isFinal: true);
+      h.run([
+        localFunction([
+          declareInitialized(b, expr('bool').or(expr('bool'))),
+          declare(i, initialized: false),
+          if_(b.expr, [
+            checkUnassigned(i, true),
+            i.write(expr('int')).stmt,
+          ], [
+            checkUnassigned(i, true),
+            i.write(expr('int')).stmt,
+          ]),
+        ]),
+      ]);
+    });
   });
 
   group('Reachability', () {
diff --git a/tests/language/final/initialize_inside_closure_test.dart b/tests/language/final/initialize_inside_closure_test.dart
new file mode 100644
index 00000000000..f8fbcc86917
--- /dev/null
+++ b/tests/language/final/initialize_inside_closure_test.dart
@@ -0,0 +1,20 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Regression test - see https://github.com/dart-lang/sdk/issues/47991
+
+import 'dart:math';
+
+void main() {
+  () {
+    final should = Random().nextBool() || Random().nextBool();
+    final int a;
+
+    if (should) {
+      a = 1;
+    } else {
+      a = 2;
+    }
+  };
+}