diff --git a/.idea/runConfigurations/All_Tests.xml b/.idea/runConfigurations/All_Tests.xml
index 80abd8cce40..6ebba66deda 100644
--- a/.idea/runConfigurations/All_Tests.xml
+++ b/.idea/runConfigurations/All_Tests.xml
@@ -13,7 +13,7 @@
     <option name="MAIN_CLASS_NAME" value="" />
     <option name="METHOD_NAME" value="" />
     <option name="TEST_OBJECT" value="package" />
-    <option name="VM_PARAMETERS" value="" />
+    <option name="VM_PARAMETERS" value="-ea" />
     <option name="PARAMETERS" value="" />
     <option name="WORKING_DIRECTORY" value="file://$PROJECT_DIR$" />
     <option name="ENV_VARIABLES" />
diff --git a/idea/src/org/jetbrains/jet/JetNodeTypes.java b/idea/src/org/jetbrains/jet/JetNodeTypes.java
index 8fab0c1cb73..ff21e5e4ed1 100644
--- a/idea/src/org/jetbrains/jet/JetNodeTypes.java
+++ b/idea/src/org/jetbrains/jet/JetNodeTypes.java
@@ -117,7 +117,7 @@ public interface JetNodeTypes {
     JetNodeType ROOT_NAMESPACE            = new JetNodeType("ROOT_NAMESPACE", JetRootNamespaceExpression.class);
     JetNodeType DECOMPOSER_ARGUMENT_LIST  = new JetNodeType("DECOMPOSER_ARGUMENT_LIST");
     JetNodeType DECOMPOSER_ARGUMENT       = new JetNodeType("DECOMPOSER_ARGUMENT");
-    JetNodeType TYPE_PATTERN              = new JetNodeType("TYPE_PATTERN");
+    JetNodeType TYPE_PATTERN              = new JetNodeType("TYPE_PATTERN", JetTypePattern.class);
     JetNodeType EXPRESSION_PATTERN        = new JetNodeType("EXPRESSION_PATTERN");
     JetNodeType BINDING_PATTERN           = new JetNodeType("BINDING_PATTERN");
     JetNodeType WILDCARD_PATTERN          = new JetNodeType("WILDCARD_PATTERN");
diff --git a/idea/src/org/jetbrains/jet/lang/cfg/JetControlFlowProcessor.java b/idea/src/org/jetbrains/jet/lang/cfg/JetControlFlowProcessor.java
index 6e52be0a950..923bbe808a2 100644
--- a/idea/src/org/jetbrains/jet/lang/cfg/JetControlFlowProcessor.java
+++ b/idea/src/org/jetbrains/jet/lang/cfg/JetControlFlowProcessor.java
@@ -601,6 +601,14 @@ public class JetControlFlowProcessor {
             builder.read(expression);
         }
 
+
+        @Override
+        public void visitIsExpression(JetIsExpression expression) {
+            value(expression.getLeftHandSide(), false, inCondition);
+            // TODO : builder.read(expression.getPattern());
+            builder.read(expression);
+        }
+
         @Override
         public void visitTypeProjection(JetTypeProjection typeProjection) {
             // TODO : Support Type Arguments. Class object may be initialized at this point");
diff --git a/idea/src/org/jetbrains/jet/lang/psi/JetIsExpression.java b/idea/src/org/jetbrains/jet/lang/psi/JetIsExpression.java
index e4d7b426aa9..a4e8ffb2a33 100644
--- a/idea/src/org/jetbrains/jet/lang/psi/JetIsExpression.java
+++ b/idea/src/org/jetbrains/jet/lang/psi/JetIsExpression.java
@@ -2,6 +2,7 @@ package org.jetbrains.jet.lang.psi;
 
 import com.intellij.lang.ASTNode;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * @author abreslav
@@ -15,4 +16,15 @@ public class JetIsExpression extends JetExpression {
     public void accept(JetVisitor visitor) {
         visitor.visitIsExpression(this);
     }
+
+    @NotNull
+    public JetExpression getLeftHandSide() {
+        return findChildByClass(JetExpression.class);
+    }
+
+    @Nullable @IfNotParsed
+    public JetPattern getPattern() {
+        return findChildByClass(JetPattern.class);
+    }
+
 }
diff --git a/idea/src/org/jetbrains/jet/lang/psi/JetPattern.java b/idea/src/org/jetbrains/jet/lang/psi/JetPattern.java
new file mode 100644
index 00000000000..4c8d03ebec9
--- /dev/null
+++ b/idea/src/org/jetbrains/jet/lang/psi/JetPattern.java
@@ -0,0 +1,13 @@
+package org.jetbrains.jet.lang.psi;
+
+import com.intellij.lang.ASTNode;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * @author abreslav
+ */
+public class JetPattern extends JetElement {
+    public JetPattern(@NotNull ASTNode node) {
+        super(node);
+    }
+}
diff --git a/idea/src/org/jetbrains/jet/lang/psi/JetTypePattern.java b/idea/src/org/jetbrains/jet/lang/psi/JetTypePattern.java
new file mode 100644
index 00000000000..acec30077f3
--- /dev/null
+++ b/idea/src/org/jetbrains/jet/lang/psi/JetTypePattern.java
@@ -0,0 +1,19 @@
+package org.jetbrains.jet.lang.psi;
+
+import com.intellij.lang.ASTNode;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+/**
+ * @author abreslav
+ */
+public class JetTypePattern extends JetPattern {
+    public JetTypePattern(@NotNull ASTNode node) {
+        super(node);
+    }
+
+    @Nullable @IfNotParsed
+    public JetTypeReference getTypeReference() {
+        return findChildByClass(JetTypeReference.class);
+    }
+}
diff --git a/idea/src/org/jetbrains/jet/lang/types/JetTypeInferrer.java b/idea/src/org/jetbrains/jet/lang/types/JetTypeInferrer.java
index 807c2c002e9..6b9a295fc09 100644
--- a/idea/src/org/jetbrains/jet/lang/types/JetTypeInferrer.java
+++ b/idea/src/org/jetbrains/jet/lang/types/JetTypeInferrer.java
@@ -864,6 +864,8 @@ public class JetTypeInferrer {
             }
         }
 
+
+
         @Override
         public void visitTupleExpression(JetTupleExpression expression) {
             List<JetExpression> entries = expression.getEntries();
@@ -1255,6 +1257,19 @@ public class JetTypeInferrer {
         @Override
         public void visitIsExpression(JetIsExpression expression) {
             // TODO : patterns and everything
+            JetType knownType = getType(scope, expression.getLeftHandSide(), false);
+            JetPattern pattern = expression.getPattern();
+            if (pattern instanceof JetTypePattern) {
+                JetTypePattern typePattern = (JetTypePattern) pattern;
+                JetTypeReference typeReference = typePattern.getTypeReference();
+                if (typeReference != null && knownType != null) {
+                    JetType targetType = typeResolver.resolveType(scope, typeReference);
+                    if (!semanticServices.getTypeChecker().isSubtypeOf(targetType, knownType)) {
+                        trace.getErrorHandler().genericWarning(expression.getNode(), "Expression always evaluates to false"); // TODO : make an error?
+                    }
+                }
+
+            }
             result = semanticServices.getStandardLibrary().getBooleanType();
         }
 
diff --git a/idea/testData/checker/IsExpressions.jet b/idea/testData/checker/IsExpressions.jet
new file mode 100644
index 00000000000..a88f9578186
--- /dev/null
+++ b/idea/testData/checker/IsExpressions.jet
@@ -0,0 +1,7 @@
+fun test() {
+   if (1 is Int) {
+     if (<warning>1 is Boolean</warning>) {
+
+     }
+   }
+}
\ No newline at end of file