diff --git a/compiler/testData/diagnostics/tests/inference/NoInferenceFromDeclaredBounds.kt b/compiler/testData/diagnostics/tests/inference/NoInferenceFromDeclaredBounds.kt
index 769fa72bd6a..031a8581e01 100644
--- a/compiler/testData/diagnostics/tests/inference/NoInferenceFromDeclaredBounds.kt
+++ b/compiler/testData/diagnostics/tests/inference/NoInferenceFromDeclaredBounds.kt
@@ -6,4 +6,6 @@ fun foo1() {
     <!TYPE_INFERENCE_NO_INFORMATION_FOR_PARAMETER!>fooT22<!>()
 }
 
-val n : Nothing = null.sure()
\ No newline at end of file
+val n : Nothing = null!!
+
+fun <T : Any> T?.sure() : T = this!!
diff --git a/compiler/testData/diagnostics/tests/inference/regressions/kt1358.kt b/compiler/testData/diagnostics/tests/inference/regressions/kt1358.kt
index 395bf4371ae..5c28166bb42 100644
--- a/compiler/testData/diagnostics/tests/inference/regressions/kt1358.kt
+++ b/compiler/testData/diagnostics/tests/inference/regressions/kt1358.kt
@@ -8,4 +8,5 @@ fun bar(a: Any?) {
     }
 }
 
-fun <T : Any> T?.foo() {}
\ No newline at end of file
+fun <T : Any> T?.foo() {}
+fun <T : Any> T?.sure() : T = this!!
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/inference/regressions/kt1558.kt b/compiler/testData/diagnostics/tests/inference/regressions/kt1558.kt
index 6f1a50b4e29..2ec9436e4a2 100644
--- a/compiler/testData/diagnostics/tests/inference/regressions/kt1558.kt
+++ b/compiler/testData/diagnostics/tests/inference/regressions/kt1558.kt
@@ -1,7 +1,9 @@
 //KT-1558 Exception while analyzing
 package j
 
-fun testArrays(val ci: List<Int?>, val cii: List<Int?>) {
+fun <T : Any> T?.sure() : T = this!!
+
+fun testArrays(val ci: List<Int?>, val cii: List<Int?>?) {
     val c1: Array<Int?> = cii.sure().toArray(<!FUNCTION_CALL_EXPECTED!><!NO_VALUE_FOR_PARAMETER, NO_VALUE_FOR_PARAMETER!>Array<!><Int?><!>)
 
     val c2: Array<Int?> = ci.toArray(Array<Int?><!NO_VALUE_FOR_PARAMETER, NO_VALUE_FOR_PARAMETER!>()<!>)
diff --git a/compiler/testData/diagnostics/tests/inference/regressions/kt742.kt b/compiler/testData/diagnostics/tests/inference/regressions/kt742.kt
index 1e32ffc67a0..d8f1846148c 100644
--- a/compiler/testData/diagnostics/tests/inference/regressions/kt742.kt
+++ b/compiler/testData/diagnostics/tests/inference/regressions/kt742.kt
@@ -1,6 +1,8 @@
 //KT-742 Stack overflow in type inference
 package a
 
+fun <T : Any> T?.sure() : T = this!!
+
 class List<T>(val head: T, val tail: List<T>? = null)
 
 fun <T, Q> List<T>.map1(f: (T)-> Q): List<T>? = tail!!.map1(f)
diff --git a/compiler/testData/diagnostics/tests/inference/regressions/kt943.kt b/compiler/testData/diagnostics/tests/inference/regressions/kt943.kt
index ed0987b815f..2df5de1d2f4 100644
--- a/compiler/testData/diagnostics/tests/inference/regressions/kt943.kt
+++ b/compiler/testData/diagnostics/tests/inference/regressions/kt943.kt
@@ -15,4 +15,6 @@ fun foo(lines: List<String>) {
 }
 
 //standard library
+fun <T : Any> T?.sure() : T = this!!
+
 public inline fun <T> comparator(<!UNUSED_PARAMETER!>fn<!>: (T,T) -> Int): Comparator<T> {<!NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY!>}<!>
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/regressions/kt557.kt b/compiler/testData/diagnostics/tests/regressions/kt557.kt
index 4ac9a61049c..993d2703426 100644
--- a/compiler/testData/diagnostics/tests/regressions/kt557.kt
+++ b/compiler/testData/diagnostics/tests/regressions/kt557.kt
@@ -1,5 +1,7 @@
 // KT-557 Wrong type inference near sure extension function
 
+fun <T : Any> T?.sure() : T = this!!
+
 fun Array<String>.length() : Int {
     return 0;
 }
diff --git a/compiler/testData/diagnostics/tests/regressions/kt630.kt b/compiler/testData/diagnostics/tests/regressions/kt630.kt
index 2b26b0faa1e..2cef7f519a8 100644
--- a/compiler/testData/diagnostics/tests/regressions/kt630.kt
+++ b/compiler/testData/diagnostics/tests/regressions/kt630.kt
@@ -1,3 +1,6 @@
 // KT-630 Bad type inference
+
+fun <T : Any> T?.sure() : T = this!!
+
 val x = "lala".sure()
 val s : String = x
diff --git a/compiler/testData/diagnostics/tests/regressions/kt743.kt b/compiler/testData/diagnostics/tests/regressions/kt743.kt
index f508c0af0bd..4d29b36c57d 100644
--- a/compiler/testData/diagnostics/tests/regressions/kt743.kt
+++ b/compiler/testData/diagnostics/tests/regressions/kt743.kt
@@ -1,5 +1,7 @@
 //KT-743 Wrong type inference
 class List<T>(val head: T, val tail: List<T>? = null)
 
+fun <T : Any> T?.sure() : T = this!!
+
 fun <T, Q> List<T>.map(f: (T)-> Q): List<T>? = tail.sure<List<T>>().map(f)
 fun foo<T>(t : T) : T = foo(t)
diff --git a/compiler/testData/diagnostics/tests/regressions/kt750.kt b/compiler/testData/diagnostics/tests/regressions/kt750.kt
index dbbf53c08bb..b37f565ee9c 100644
--- a/compiler/testData/diagnostics/tests/regressions/kt750.kt
+++ b/compiler/testData/diagnostics/tests/regressions/kt750.kt
@@ -3,6 +3,8 @@ fun main(args : Array<String>) {
   var i : Int? = Integer.valueOf(100)
   var s : Int? = Integer.valueOf(100)
 
-  val o = i .sure() + s.sure()
+  val o = i.sure() + s.sure()
   System.out.println(o)
 }
+
+fun <T : Any> T?.sure() : T = this!!