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 c5aff27be5c..e9984635f3a 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
@@ -267,9 +267,15 @@ public class ConstraintSystemImpl implements ConstraintSystem {
 
         @Override
         public boolean noCorrespondingSupertype(@NotNull JetType subtype, @NotNull JetType supertype) {
-            // If some of the types is an unknown, the constraint is already generated, and we should carry on
+            // If some of the types is an unknown, the constraint must be generated, and we should carry on
             // otherwise there can be no solution, and we should fail
-            return someUnknown(getTypeValueFor(subtype), getTypeValueFor(supertype));
+            TypeValue subTypeValue = getTypeValueFor(subtype);
+            TypeValue superTypeValue = getTypeValueFor(supertype);
+            boolean someUnknown = someUnknown(subTypeValue, superTypeValue);
+            if (someUnknown) {
+                addSubtypingConstraintOnTypeValues(subTypeValue, superTypeValue);
+            }
+            return someUnknown;
         }
 
         private boolean someUnknown(TypeValue subtypeValue, TypeValue supertypeValue) {
diff --git a/compiler/testData/checkerWithErrorTypes/quick/regressions/kt630.jet b/compiler/testData/checkerWithErrorTypes/quick/regressions/kt630.jet
new file mode 100644
index 00000000000..840941d9807
--- /dev/null
+++ b/compiler/testData/checkerWithErrorTypes/quick/regressions/kt630.jet
@@ -0,0 +1,3 @@
+// KT-630 Bad type inference
+val x = "lala".sure()
+val s : String = x
\ No newline at end of file