diff --git a/compiler/frontend/src/org/jetbrains/kotlin/contracts/EffectSystem.kt b/compiler/frontend/src/org/jetbrains/kotlin/contracts/EffectSystem.kt
index 4d0951cc7d8..14af3f26369 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/contracts/EffectSystem.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/contracts/EffectSystem.kt
@@ -132,7 +132,7 @@ class EffectSystem(
     }
 
     private fun getNonTrivialComputation(expression: KtExpression, trace: BindingTrace, moduleDescriptor: ModuleDescriptor): Computation? {
-        val visitor = EffectsExtractingVisitor(trace, moduleDescriptor, dataFlowValueFactory, constants)
+        val visitor = EffectsExtractingVisitor(trace, moduleDescriptor, dataFlowValueFactory, constants, languageVersionSettings)
         return visitor.extractOrGetCached(expression).takeUnless { it == UNKNOWN_COMPUTATION }
     }
 }
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/contracts/EffectsExtractingVisitor.kt b/compiler/frontend/src/org/jetbrains/kotlin/contracts/EffectsExtractingVisitor.kt
index 0b9dfb0b543..a1b2435d951 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/contracts/EffectsExtractingVisitor.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/contracts/EffectsExtractingVisitor.kt
@@ -17,6 +17,8 @@
 package org.jetbrains.kotlin.contracts
 
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
+import org.jetbrains.kotlin.config.LanguageFeature
+import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.contracts.description.ContractProviderKey
 import org.jetbrains.kotlin.contracts.model.Computation
 import org.jetbrains.kotlin.contracts.model.ConditionalEffect
@@ -56,7 +58,8 @@ class EffectsExtractingVisitor(
     private val trace: BindingTrace,
     private val moduleDescriptor: ModuleDescriptor,
     private val dataFlowValueFactory: DataFlowValueFactory,
-    private val constants: ESConstants
+    private val constants: ESConstants,
+    private val languageVersionSettings: LanguageVersionSettings
 ) : KtVisitor<Computation, Unit>() {
     private val builtIns: KotlinBuiltIns get() = moduleDescriptor.builtIns
 
@@ -162,7 +165,13 @@ class EffectsExtractingVisitor(
 
     private fun ReceiverValue.toComputation(): Computation = when (this) {
         is ExpressionReceiver -> extractOrGetCached(expression)
-        is ExtensionReceiver -> ESReceiverWithDataFlowValue(this, createDataFlowValue())
+        is ExtensionReceiver -> {
+            if (languageVersionSettings.supportsFeature(LanguageFeature.ContractsOnCallsWithImplicitReceiver)) {
+                ESReceiverWithDataFlowValue(this, createDataFlowValue())
+            } else {
+                UNKNOWN_COMPUTATION
+            }
+        }
         else -> UNKNOWN_COMPUTATION
     }
 
diff --git a/compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver.kt b/compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver.kt
index d84019d08ba..f34b254d12c 100644
--- a/compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver.kt
+++ b/compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver.kt
@@ -20,7 +20,7 @@ fun smartcastOnReceiver(s: String?) {
             <!UNSAFE_CALL!>length<!>
         }
         else {
-            <!DEBUG_INFO_IMPLICIT_RECEIVER_SMARTCAST!>length<!>
+            <!UNSAFE_CALL!>length<!>
         }
     }
 }
diff --git a/compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver_after.kt b/compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver_after.kt
new file mode 100644
index 00000000000..3e0213fe764
--- /dev/null
+++ b/compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver_after.kt
@@ -0,0 +1,38 @@
+// !LANGUAGE: +AllowContractsForCustomFunctions +UseReturnsEffect +ContractsOnCallsWithImplicitReceiver
+// !USE_EXPERIMENTAL: kotlin.contracts.ExperimentalContracts
+// !DIAGNOSTICS: -INVISIBLE_REFERENCE -INVISIBLE_MEMBER
+//
+// ISSUE: KT-28672
+
+import kotlin.contracts.*
+
+fun CharSequence?.isNullOrEmpty(): Boolean {
+    contract {
+        returns(false) implies (this@isNullOrEmpty != null)
+    }
+
+    return this == null || <!DEBUG_INFO_SMARTCAST!>this<!>.length == 0
+}
+
+fun smartcastOnReceiver(s: String?) {
+    with(s) {
+        if (isNullOrEmpty()) {
+            <!UNSAFE_CALL!>length<!>
+        }
+        else {
+            <!DEBUG_INFO_IMPLICIT_RECEIVER_SMARTCAST!>length<!>
+        }
+    }
+}
+
+fun mixedReceiver(s: String?) {
+    if (!s.isNullOrEmpty()) {
+        with(<!DEBUG_INFO_SMARTCAST!>s<!>) {
+            length
+        }
+    } else {
+        with(s) {
+            <!UNSAFE_CALL!>length<!>
+        }
+    }
+}
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver_after.txt b/compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver_after.txt
new file mode 100644
index 00000000000..8605fe32df8
--- /dev/null
+++ b/compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver_after.txt
@@ -0,0 +1,6 @@
+package
+
+public fun mixedReceiver(/*0*/ s: kotlin.String?): kotlin.Unit
+public fun smartcastOnReceiver(/*0*/ s: kotlin.String?): kotlin.Unit
+public fun kotlin.CharSequence?.isNullOrEmpty(): kotlin.Boolean
+    Returns(FALSE) -> <this> != null
diff --git a/compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestWithStdLibGenerated.java b/compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestWithStdLibGenerated.java
index a913f6217a8..8d730246ec6 100644
--- a/compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestWithStdLibGenerated.java
+++ b/compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestWithStdLibGenerated.java
@@ -1301,6 +1301,11 @@ public class DiagnosticsTestWithStdLibGenerated extends AbstractDiagnosticsTestW
                 runTest("compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver.kt");
             }
 
+            @TestMetadata("extensionReceiver_after.kt")
+            public void testExtensionReceiver_after() throws Exception {
+                runTest("compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver_after.kt");
+            }
+
             @TestMetadata("intersectingInfo.kt")
             public void testIntersectingInfo() throws Exception {
                 runTest("compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/intersectingInfo.kt");
diff --git a/compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsTestWithStdLibUsingJavacGenerated.java b/compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsTestWithStdLibUsingJavacGenerated.java
index 990b63e6031..70a946a7a95 100644
--- a/compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsTestWithStdLibUsingJavacGenerated.java
+++ b/compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsTestWithStdLibUsingJavacGenerated.java
@@ -1301,6 +1301,11 @@ public class DiagnosticsTestWithStdLibUsingJavacGenerated extends AbstractDiagno
                 runTest("compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver.kt");
             }
 
+            @TestMetadata("extensionReceiver_after.kt")
+            public void testExtensionReceiver_after() throws Exception {
+                runTest("compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver_after.kt");
+            }
+
             @TestMetadata("intersectingInfo.kt")
             public void testIntersectingInfo() throws Exception {
                 runTest("compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/intersectingInfo.kt");
diff --git a/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt b/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
index 0f0da571a48..050ede35d7e 100644
--- a/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
+++ b/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
@@ -121,6 +121,7 @@ enum class LanguageFeature(
 
     InlineClasses(sinceVersion = KOTLIN_1_3, defaultState = State.ENABLED_WITH_WARNING, kind = UNSTABLE_FEATURE),
 
+    ContractsOnCallsWithImplicitReceiver(sinceVersion = KOTLIN_1_3, defaultState = State.DISABLED),
     ;
 
     val presentableName: String