diff --git a/idea/src/org/jetbrains/jet/lang/cfg/JetControlFlowProcessor.java b/idea/src/org/jetbrains/jet/lang/cfg/JetControlFlowProcessor.java
index 3b62afcb70a..be753b341f1 100644
--- a/idea/src/org/jetbrains/jet/lang/cfg/JetControlFlowProcessor.java
+++ b/idea/src/org/jetbrains/jet/lang/cfg/JetControlFlowProcessor.java
@@ -649,12 +649,25 @@ public class JetControlFlowProcessor {
 
                         @Override
                         public void visitWhenConditionIsPattern(JetWhenConditionIsPattern condition) {
-                            super.visitWhenConditionIsPattern(condition); // TODO
+                            JetPattern pattern = condition.getPattern();
+                            if (pattern != null) {
+                                pattern.accept(new JetVisitor() {
+                                    @Override
+                                    public void visitTypePattern(JetTypePattern typePattern) {
+                                        // TODO
+                                    }
+
+                                    @Override
+                                    public void visitJetElement(JetElement elem) {
+                                        throw new UnsupportedOperationException(elem.toString());
+                                    }
+                                });
+                            }
                         }
 
                         @Override
                         public void visitJetElement(JetElement elem) {
-                            throw new UnsupportedOperationException();
+                            throw new UnsupportedOperationException(elem.toString());
                         }
                     });
                 }
diff --git a/idea/src/org/jetbrains/jet/lang/psi/JetTypePattern.java b/idea/src/org/jetbrains/jet/lang/psi/JetTypePattern.java
index acec30077f3..08bb92a47cd 100644
--- a/idea/src/org/jetbrains/jet/lang/psi/JetTypePattern.java
+++ b/idea/src/org/jetbrains/jet/lang/psi/JetTypePattern.java
@@ -16,4 +16,9 @@ public class JetTypePattern extends JetPattern {
     public JetTypeReference getTypeReference() {
         return findChildByClass(JetTypeReference.class);
     }
+
+    @Override
+    public void accept(@NotNull JetVisitor visitor) {
+        visitor.visitTypePattern(this);
+    }
 }
diff --git a/idea/src/org/jetbrains/jet/lang/psi/JetVisitor.java b/idea/src/org/jetbrains/jet/lang/psi/JetVisitor.java
index 1f9d202dcc9..b347d15176a 100644
--- a/idea/src/org/jetbrains/jet/lang/psi/JetVisitor.java
+++ b/idea/src/org/jetbrains/jet/lang/psi/JetVisitor.java
@@ -365,4 +365,12 @@ public class JetVisitor extends PsiElementVisitor {
     public void visitWhenConditionInRange(JetWhenConditionInRange condition) {
         visitJetElement(condition);
     }
+
+    public void visitTypePattern(JetTypePattern typePattern) {
+        visitPattern(typePattern);
+    }
+
+    public void visitPattern(JetPattern pattern) {
+        visitJetElement(pattern);
+    }
 }
diff --git a/idea/src/org/jetbrains/jet/lang/types/JetTypeInferrer.java b/idea/src/org/jetbrains/jet/lang/types/JetTypeInferrer.java
index 1e48186c714..4263ef7523a 100644
--- a/idea/src/org/jetbrains/jet/lang/types/JetTypeInferrer.java
+++ b/idea/src/org/jetbrains/jet/lang/types/JetTypeInferrer.java
@@ -1019,7 +1019,26 @@ public class JetTypeInferrer {
 
                         @Override
                         public void visitWhenConditionIsPattern(JetWhenConditionIsPattern condition) {
-                            super.visitWhenConditionIsPattern(condition); // TODO
+                            JetPattern pattern = condition.getPattern();
+                            if (pattern != null) {
+                                pattern.accept(new JetVisitor() {
+                                    @Override
+                                    public void visitTypePattern(JetTypePattern typePattern) {
+                                        JetTypeReference typeReference = typePattern.getTypeReference();
+                                        if (typeReference != null) {
+                                            JetType type = typeResolver.resolveType(scope, typeReference);
+                                            if (TypeUtils.intersect(semanticServices.getTypeChecker(), Sets.newHashSet(type, finalSubjectType)) == null) {
+                                                trace.getErrorHandler().genericError(typePattern.getNode(), "Incompatible types"); // TODO : message
+                                            }
+                                        }
+                                    }
+
+                                    @Override
+                                    public void visitJetElement(JetElement elem) {
+                                        trace.getErrorHandler().genericError(elem.getNode(), "Unsupported [JetTypeInferrer]");
+                                    }
+                                });
+                            }
                         }
 
                         @Override
diff --git a/idea/testData/checker/When.jet b/idea/testData/checker/When.jet
index 7eb6e6b582f..13a68794b33 100644
--- a/idea/testData/checker/When.jet
+++ b/idea/testData/checker/When.jet
@@ -2,6 +2,9 @@ fun foo() {
     val s = ""
     val x = 1
     when (x) {
+      is <error>String</error> => 1
+      !is Int => 1
+      is Any? => 1
       <error>s</error> => 1
       1 => 1
       1 + <error>a</error> => 1