diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/types/TypeUtils.java b/compiler/frontend/src/org/jetbrains/jet/lang/types/TypeUtils.java
index 82e4416c056..33a4211e2af 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/types/TypeUtils.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/types/TypeUtils.java
@@ -343,6 +343,11 @@ public class TypeUtils {
     private static void fillInDeepSubstitutor(@NotNull JetType context, @NotNull TypeSubstitutor substitutor, @NotNull Map<TypeConstructor, TypeProjection> substitution, @Nullable Multimap<TypeConstructor, TypeProjection> fullSubstitution) {
         List<TypeParameterDescriptor> parameters = context.getConstructor().getParameters();
         List<TypeProjection> arguments = context.getArguments();
+        
+        if (parameters.size() != arguments.size()) {
+            throw new IllegalStateException();
+        }
+        
         for (int i = 0; i < arguments.size(); i++) {
             TypeProjection argument = arguments.get(i);
             TypeParameterDescriptor typeParameterDescriptor = parameters.get(i);
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/BasicExpressionTypingVisitor.java b/compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/BasicExpressionTypingVisitor.java
index 475acc8f65e..7b64af7a06b 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/BasicExpressionTypingVisitor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/BasicExpressionTypingVisitor.java
@@ -266,6 +266,11 @@ public class BasicExpressionTypingVisitor extends ExpressionTypingVisitor {
             return false;
         }
 
+        // do not crash on error types
+        if (ErrorUtils.isErrorType(actualType) || ErrorUtils.isErrorType(targetType)) {
+            return false;
+        }
+
         {
             Multimap<TypeConstructor, TypeProjection> typeSubstitutionMap =
                     TypeUtils.buildDeepSubstitutionMultimap(targetType);
diff --git a/compiler/testData/diagnostics/tests/cast/IsErasedAllow.jet b/compiler/testData/diagnostics/tests/cast/IsErasedAllowSameClassParameter.jet
similarity index 100%
rename from compiler/testData/diagnostics/tests/cast/IsErasedAllow.jet
rename to compiler/testData/diagnostics/tests/cast/IsErasedAllowSameClassParameter.jet
diff --git a/compiler/testData/diagnostics/tests/cast/IsErasedAllowSameParameterParameter.jet b/compiler/testData/diagnostics/tests/cast/IsErasedAllowSameParameterParameter.jet
new file mode 100644
index 00000000000..6d6e453858b
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/cast/IsErasedAllowSameParameterParameter.jet
@@ -0,0 +1,7 @@
+// +JDK
+
+import java.util.Collection;
+import java.util.List;
+
+fun ff<T>(l: Collection<T>) = l is List<T>
+