diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/types/inference/ConstraintSystemImpl.java b/compiler/frontend/src/org/jetbrains/jet/lang/types/inference/ConstraintSystemImpl.java
index a569a0beb1f..30f28d9ffa7 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/types/inference/ConstraintSystemImpl.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/types/inference/ConstraintSystemImpl.java
@@ -376,6 +376,7 @@ public class ConstraintSystemImpl implements ConstraintSystem {
                 DeclarationDescriptor declarationDescriptor = key.getDeclarationDescriptor();
                 if (declarationDescriptor instanceof TypeParameterDescriptor) {
                     TypeParameterDescriptor descriptor = (TypeParameterDescriptor) declarationDescriptor;
+                    if (!unknownTypes.containsKey(descriptor)) return null;
                     println(descriptor + " |-> " + getValue(descriptor));
                     return new TypeProjection(getValue(descriptor));
                 }
diff --git a/compiler/testData/checkerWithErrorTypes/full/regression/kt335.336.jet b/compiler/testData/checkerWithErrorTypes/full/regression/kt335.336.jet
new file mode 100644
index 00000000000..46537f0041c
--- /dev/null
+++ b/compiler/testData/checkerWithErrorTypes/full/regression/kt335.336.jet
@@ -0,0 +1,14 @@
+// KT-336 Can't infer type parameter for ArrayList in a generic function (Exception in type inference)
+// KT-335 Type inference fails on Collections.sort
+
+import java.util.*
+import java.lang.Comparable as Comparable
+
+fun <T : java.lang.Comparable<T>> List<T>.sort() {
+  Collections.sort(this) // Error here
+}
+
+fun <T> List<T>.plus(other : List<T>) : List<T> {
+  val result = ArrayList(this)
+  return result
+}