diff --git a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java
index f83afdbc928..1cf63e3a562 100644
--- a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java
+++ b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java
@@ -11472,6 +11472,12 @@ public class DiagnosisCompilerTestFE10TestdataTestGenerated extends AbstractDiag
                 runTest("compiler/testData/diagnostics/tests/functionLiterals/kt47493.kt");
             }
 
+            @Test
+            @TestMetadata("kt51317.kt")
+            public void testKt51317() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/functionLiterals/kt51317.kt");
+            }
+
             @Test
             @TestMetadata("kt6541_extensionForExtensionFunction.kt")
             public void testKt6541_extensionForExtensionFunction() throws Exception {
diff --git a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java
index 66f9edfd526..89d9caad36a 100644
--- a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java
+++ b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java
@@ -11472,6 +11472,12 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                 runTest("compiler/testData/diagnostics/tests/functionLiterals/kt47493.kt");
             }
 
+            @Test
+            @TestMetadata("kt51317.kt")
+            public void testKt51317() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/functionLiterals/kt51317.kt");
+            }
+
             @Test
             @TestMetadata("kt6541_extensionForExtensionFunction.kt")
             public void testKt6541_extensionForExtensionFunction() throws Exception {
diff --git a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsWithLightTreeTestGenerated.java b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsWithLightTreeTestGenerated.java
index 3b460647613..d1ca1c8e5d0 100644
--- a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsWithLightTreeTestGenerated.java
+++ b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsWithLightTreeTestGenerated.java
@@ -11472,6 +11472,12 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                 runTest("compiler/testData/diagnostics/tests/functionLiterals/kt47493.kt");
             }
 
+            @Test
+            @TestMetadata("kt51317.kt")
+            public void testKt51317() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/functionLiterals/kt51317.kt");
+            }
+
             @Test
             @TestMetadata("kt6541_extensionForExtensionFunction.kt")
             public void testKt6541_extensionForExtensionFunction() throws Exception {
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/kt51317.fir.kt b/compiler/testData/diagnostics/tests/functionLiterals/kt51317.fir.kt
new file mode 100644
index 00000000000..fa6d1df9fb9
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/functionLiterals/kt51317.fir.kt
@@ -0,0 +1,11 @@
+val f: (String.() -> String)? = null
+
+fun box(): String {
+    val g = when {
+        f != null -> f
+        else -> {
+            { this + "K" }
+        }
+    }
+    return g("O")
+}
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/kt51317.kt b/compiler/testData/diagnostics/tests/functionLiterals/kt51317.kt
new file mode 100644
index 00000000000..70738728d97
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/functionLiterals/kt51317.kt
@@ -0,0 +1,11 @@
+val f: (String.() -> String)? = null
+
+fun box(): String {
+    val g = when {
+        f != null -> <!DEBUG_INFO_SMARTCAST!>f<!>
+        else -> {
+            { this + "K" }
+        }
+    }
+    return g("O")
+}
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/kt51317.txt b/compiler/testData/diagnostics/tests/functionLiterals/kt51317.txt
new file mode 100644
index 00000000000..b206c621f76
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/functionLiterals/kt51317.txt
@@ -0,0 +1,4 @@
+package
+
+public val f: (kotlin.String.() -> kotlin.String)? = null
+public fun box(): kotlin.String
diff --git a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java
index da24f25ea43..ba0893ea89a 100644
--- a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java
+++ b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java
@@ -11478,6 +11478,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/functionLiterals/kt47493.kt");
             }
 
+            @Test
+            @TestMetadata("kt51317.kt")
+            public void testKt51317() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/functionLiterals/kt51317.kt");
+            }
+
             @Test
             @TestMetadata("kt6541_extensionForExtensionFunction.kt")
             public void testKt6541_extensionForExtensionFunction() throws Exception {
diff --git a/core/descriptors/src/org/jetbrains/kotlin/types/AnnotationsTypeAttribute.kt b/core/descriptors/src/org/jetbrains/kotlin/types/AnnotationsTypeAttribute.kt
index d4379c4d0ff..5a8cda10f3e 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/types/AnnotationsTypeAttribute.kt
+++ b/core/descriptors/src/org/jetbrains/kotlin/types/AnnotationsTypeAttribute.kt
@@ -10,9 +10,11 @@ import org.jetbrains.kotlin.descriptors.annotations.composeAnnotations
 import kotlin.reflect.KClass
 
 class AnnotationsTypeAttribute(val annotations: Annotations) : TypeAttribute<AnnotationsTypeAttribute>() {
-    override fun union(other: AnnotationsTypeAttribute?): AnnotationsTypeAttribute? = null
+    override fun union(other: AnnotationsTypeAttribute?): AnnotationsTypeAttribute? =
+        if (other == this) this else null
 
-    override fun intersect(other: AnnotationsTypeAttribute?): AnnotationsTypeAttribute? = null
+    override fun intersect(other: AnnotationsTypeAttribute?): AnnotationsTypeAttribute? =
+        if (other == this) this else null
 
     override fun add(other: AnnotationsTypeAttribute?): AnnotationsTypeAttribute {
         if (other == null) return this
@@ -23,6 +25,13 @@ class AnnotationsTypeAttribute(val annotations: Annotations) : TypeAttribute<Ann
 
     override val key: KClass<out AnnotationsTypeAttribute>
         get() = AnnotationsTypeAttribute::class
+
+    override fun equals(other: Any?): Boolean {
+        if (other !is AnnotationsTypeAttribute) return false
+        return other.annotations == this.annotations
+    }
+
+    override fun hashCode(): Int = annotations.hashCode()
 }
 
 val TypeAttributes.annotationsAttribute: AnnotationsTypeAttribute? by TypeAttributes.attributeAccessor<AnnotationsTypeAttribute>()