diff --git a/sdk/lib/_internal/compiler/implementation/inferrer/inferrer_visitor.dart b/sdk/lib/_internal/compiler/implementation/inferrer/inferrer_visitor.dart
index 86662f7..94d80bb 100644
--- a/sdk/lib/_internal/compiler/implementation/inferrer/inferrer_visitor.dart
+++ b/sdk/lib/_internal/compiler/implementation/inferrer/inferrer_visitor.dart
@@ -842,14 +842,19 @@
     } else if ("&&" == op.source) {
       conditionIsSimple = false;
       bool oldAccumulateIsChecks = accumulateIsChecks;
-      accumulateIsChecks = true;
-      if (isChecks == null) isChecks = <Send>[];
+      List<Send> oldIsChecks = isChecks;
+      if (!accumulateIsChecks) {
+        accumulateIsChecks = true;
+        isChecks = <Send>[];
+      }
       visit(node.receiver);
-      accumulateIsChecks = oldAccumulateIsChecks;
-      if (!accumulateIsChecks) isChecks = null;
       LocalsHandler<T> saved = locals;
       locals = new LocalsHandler<T>.from(locals, node);
       updateIsChecks(isChecks, usePositive: true);
+      if (!oldAccumulateIsChecks) {
+        accumulateIsChecks = false;
+        isChecks = oldIsChecks;
+      }
       visit(node.arguments.head);
       saved.mergeDiamondFlow(locals, null);
       locals = saved;
@@ -857,10 +862,10 @@
     } else if ("||" == op.source) {
       conditionIsSimple = false;
       List<Send> tests = <Send>[];
-      handleCondition(node.receiver, tests);
+      bool isSimple = handleCondition(node.receiver, tests);
       LocalsHandler<T> saved = locals;
       locals = new LocalsHandler<T>.from(locals, node);
-      updateIsChecks(tests, usePositive: false);
+      if (isSimple) updateIsChecks(tests, usePositive: false);
       bool oldAccumulateIsChecks = accumulateIsChecks;
       accumulateIsChecks = false;
       visit(node.arguments.head);
diff --git a/tests/compiler/dart2js/simple_inferrer_and_or_test.dart b/tests/compiler/dart2js/simple_inferrer_and_or_test.dart
index 97531a6..dea4f69 100644
--- a/tests/compiler/dart2js/simple_inferrer_and_or_test.dart
+++ b/tests/compiler/dart2js/simple_inferrer_and_or_test.dart
@@ -45,6 +45,39 @@
   return a;
 }
 
+returnDyn7b(x) => x;
+
+returnDyn7() {
+  var a = "foo";
+  if (a.length == 3) a = 52;
+  if ((a is int) || (a is String && true)) returnDyn7b(a);
+  return a;
+}
+
+returnDyn8(x) => x;
+
+test8() {
+  var a = "foo";
+  if (a.length == 3) a = 52;
+  if ((false && a is! String) || returnDyn8(a)) return a;
+}
+
+returnDyn9(x) => x;
+
+test9() {
+  var a = "foo";
+  if (a.length == 3) a = 52;
+  if (!(a is bool && a is bool)) returnDyn9(a);
+}
+
+returnString(x) => x;
+
+test10() {
+  var a = "foo";
+  if (a.length == 3) a = 52;
+  if (!(a is num) && a is String) returnString(a);
+}
+
 main() {
   returnDyn1();
   returnDyn2();
@@ -52,6 +85,10 @@
   returnDyn4();
   returnDyn5();
   returnDyn6();
+  returnDyn7();
+  test8();
+  test9();
+  test10();
 }
 """;
 
@@ -77,5 +114,10 @@
     checkReturn('returnDyn4', compiler.typesTask.dynamicType.nonNullable());
     checkReturn('returnDyn5', compiler.typesTask.dynamicType.nonNullable());
     checkReturn('returnDyn6', compiler.typesTask.dynamicType.nonNullable());
+    checkReturn('returnDyn7', subclassOfInterceptor);
+    checkReturn('returnDyn7b', subclassOfInterceptor);
+    checkReturn('returnDyn8', subclassOfInterceptor);
+    checkReturn('returnDyn9', subclassOfInterceptor);
+    checkReturn('returnString', compiler.typesTask.stringType);
   }));
 }
diff --git a/tests/language/logical_expression2_test.dart b/tests/language/logical_expression2_test.dart
new file mode 100644
index 0000000..7d6ddd5
--- /dev/null
+++ b/tests/language/logical_expression2_test.dart
@@ -0,0 +1,31 @@
+// Copyright (c) 2014, 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.
+
+import "package:expect/expect.dart";
+
+// Regression test for issue 17149.
+
+int globalCounter = 0;
+
+void nonInlinedUse(Object object) {
+  if (new DateTime.now().millisecondsSinceEpoch == 42) nonInlinedUse(object);
+  if (object is! String) globalCounter++;
+}
+
+int confuse(x) {
+  if (new DateTime.now().millisecondsSinceEpoch == 42) return confuse(x - 1);
+  return x;
+}
+
+main() {
+  var o = [ "foo", 499 ][confuse(1)];
+
+  // The `o is String` check in the rhs of the logical or must not be
+  // propagated to the `if` body.
+  if ((o is num) ||
+      (o is String && true)) {
+    nonInlinedUse(o);
+  }
+  Expect.equals(1, globalCounter);
+}
diff --git a/tests/language/logical_expression3_test.dart b/tests/language/logical_expression3_test.dart
new file mode 100644
index 0000000..2a90d70
--- /dev/null
+++ b/tests/language/logical_expression3_test.dart
@@ -0,0 +1,29 @@
+// Copyright (c) 2014, 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.
+
+import "package:expect/expect.dart";
+
+bool nonInlinedNumTypeCheck(Object object) {
+  if (new DateTime.now().millisecondsSinceEpoch == 42) {
+    return nonInlinedNumTypeCheck(object);
+  }
+  return object is num;
+}
+
+int confuse(x) {
+  if (new DateTime.now().millisecondsSinceEpoch == 42) return confuse(x - 1);
+  return x;
+}
+
+main() {
+  var o = [ "foo", 499 ][confuse(0)];
+
+  // When the lhs of a logical or fails, it must not assume that all negative is
+  // checks in it, have failed.
+  // Here, the `o is! num` check succeeds, but the length test failed.
+  if ((o is! num && o.length == 4) ||
+      (nonInlinedNumTypeCheck(o))) {
+    Expect.fail("Type-check failed");
+  }
+}
diff --git a/tests/language/logical_expression4_test.dart b/tests/language/logical_expression4_test.dart
new file mode 100644
index 0000000..4799a88
--- /dev/null
+++ b/tests/language/logical_expression4_test.dart
@@ -0,0 +1,27 @@
+// Copyright (c) 2014, 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.
+
+import "package:expect/expect.dart";
+
+bool nonInlinedNumTypeCheck(Object object) {
+  if (new DateTime.now().millisecondsSinceEpoch == 42) {
+    return nonInlinedNumTypeCheck(object);
+  }
+  return object is num;
+}
+
+int confuse(x) {
+  if (new DateTime.now().millisecondsSinceEpoch == 42) return confuse(x - 1);
+  return x;
+}
+
+main() {
+  var o = [ "foo", 499 ][confuse(0)];
+
+  // The is-checks in the '!' must not be propagated to the if-body.
+  // This was a bug in dart2js.
+  if (!(o is num && o is num)) {
+    Expect.isFalse((nonInlinedNumTypeCheck(o)));
+  }
+}
diff --git a/tests/language/logical_expression5_test.dart b/tests/language/logical_expression5_test.dart
new file mode 100644
index 0000000..5d983e0
--- /dev/null
+++ b/tests/language/logical_expression5_test.dart
@@ -0,0 +1,35 @@
+// Copyright (c) 2014, 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.
+
+import 'package:expect/expect.dart';
+
+bool nonInlinedNumTypeCheck(Object object) {
+  if (new DateTime.now().millisecondsSinceEpoch == 42) {
+    return nonInlinedNumTypeCheck(object);
+  }
+  return object is num;
+}
+
+bool nonInlinedStringTypeCheck(Object object) {
+  if (new DateTime.now().millisecondsSinceEpoch == 42) {
+    return nonInlinedStringTypeCheck(object);
+  }
+  return object is String;
+}
+
+int confuse(x) {
+  if (new DateTime.now().millisecondsSinceEpoch == 42) return confuse(x - 1);
+  return x;
+}
+
+main() {
+  var o = [ "foo", 499 ][confuse(0)];
+
+  // The is-checks in the '!' must not be propagated to the if-body, but
+  // the second is-check should.
+  if (!(o is num) && o is String) {
+    Expect.isFalse((nonInlinedNumTypeCheck(o)));
+    Expect.isTrue((nonInlinedStringTypeCheck(o)));
+  }
+}
diff --git a/tools/VERSION b/tools/VERSION
index d673332..b392055 100644
--- a/tools/VERSION
+++ b/tools/VERSION
@@ -28,4 +28,4 @@
 MINOR 3
 PATCH 0
 PRERELEASE 1
-PRERELEASE_PATCH 0
+PRERELEASE_PATCH 1