diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/types/SubstitutionUtils.java b/compiler/frontend/src/org/jetbrains/jet/lang/types/SubstitutionUtils.java
index 90f5e04380b..6fe27a072e6 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/types/SubstitutionUtils.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/types/SubstitutionUtils.java
@@ -95,6 +95,9 @@ public class SubstitutionUtils {
     }
 
     private static void fillInSubstitutionContext(List<TypeParameterDescriptor> parameters, List<TypeProjection> contextArguments, Map<TypeConstructor, TypeProjection> parameterValues) {
+        if (parameters.size() != contextArguments.size()) {
+            throw new IllegalArgumentException("type parameter count != context arguments");
+        }
         for (int i = 0, parametersSize = parameters.size(); i < parametersSize; i++) {
             TypeParameterDescriptor parameter = parameters.get(i);
             TypeProjection value = contextArguments.get(i);