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 bd6ae48bee8..dbd90e9b516 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
@@ -2646,6 +2646,12 @@ public class DiagnosisCompilerTestFE10TestdataTestGenerated extends AbstractDiag
                 runTest("compiler/testData/diagnostics/tests/callableReference/callableReferenceAssignmentToVar.kt");
             }
 
+            @Test
+            @TestMetadata("callableReferenceInWhenExpression.kt")
+            public void testCallableReferenceInWhenExpression() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/callableReference/callableReferenceInWhenExpression.kt");
+            }
+
             @Test
             @TestMetadata("callableReferenceWithMostSpecificGenericTypeParameter.kt")
             public void testCallableReferenceWithMostSpecificGenericTypeParameter() 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 4c53da76a9b..52487b4e638 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
@@ -2646,6 +2646,12 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                 runTest("compiler/testData/diagnostics/tests/callableReference/callableReferenceAssignmentToVar.kt");
             }
 
+            @Test
+            @TestMetadata("callableReferenceInWhenExpression.kt")
+            public void testCallableReferenceInWhenExpression() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/callableReference/callableReferenceInWhenExpression.kt");
+            }
+
             @Test
             @TestMetadata("callableReferenceWithMostSpecificGenericTypeParameter.kt")
             public void testCallableReferenceWithMostSpecificGenericTypeParameter() 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 240a4d636ac..a68aa2f137e 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
@@ -2646,6 +2646,12 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                 runTest("compiler/testData/diagnostics/tests/callableReference/callableReferenceAssignmentToVar.kt");
             }
 
+            @Test
+            @TestMetadata("callableReferenceInWhenExpression.kt")
+            public void testCallableReferenceInWhenExpression() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/callableReference/callableReferenceInWhenExpression.kt");
+            }
+
             @Test
             @TestMetadata("callableReferenceWithMostSpecificGenericTypeParameter.kt")
             public void testCallableReferenceWithMostSpecificGenericTypeParameter() throws Exception {
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/ConeTypeCompatibilityChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/ConeTypeCompatibilityChecker.kt
index f06bbf1f840..b124d2ca8ab 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/ConeTypeCompatibilityChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/ConeTypeCompatibilityChecker.kt
@@ -47,6 +47,8 @@ import org.jetbrains.kotlin.types.Variance
 object ConeTypeCompatibilityChecker {
 
     private val javaClassClassId = ClassId.fromString("java/lang/Class")
+    private val kotlinClassClassId = ClassId.fromString("kotlin/reflect/KClass")
+
 
     /**
      * The result returned by [ConeTypeCompatibilityChecker]. Note the order of enum entries matters.
@@ -134,6 +136,9 @@ object ConeTypeCompatibilityChecker {
             return Compatibility.COMPATIBLE
         }
 
+        // TODO: Due to KT-49358, we skip any checks on Java and Kotlin refection class.
+        if (upperBounds.any { it.classId == javaClassClassId || it.classId == kotlinClassClassId }) return Compatibility.COMPATIBLE
+
         val leafClassesOrInterfaces = computeLeafClassesOrInterfaces(upperBoundClasses)
         this.areClassesOrInterfacesCompatible(leafClassesOrInterfaces, compatibilityUpperBound)?.let { return it }
 
@@ -149,9 +154,6 @@ object ConeTypeCompatibilityChecker {
 
         if (upperBounds.size < 2) return Compatibility.COMPATIBLE
 
-        // TODO: Due to KT-49358, we skip any checks on Java class.
-        if (upperBounds.any { it.classId == javaClassClassId }) return Compatibility.COMPATIBLE
-
         // Base types are compatible. Now we check type parameters.
 
         val typeArgumentMapping = mutableMapOf<FirTypeParameterSymbol, BoundTypeArguments>().apply {
diff --git a/compiler/testData/diagnostics/tests/callableReference/callableReferenceInWhenExpression.kt b/compiler/testData/diagnostics/tests/callableReference/callableReferenceInWhenExpression.kt
new file mode 100644
index 00000000000..af393eeda5a
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/callableReference/callableReferenceInWhenExpression.kt
@@ -0,0 +1,18 @@
+// FIR_IDENTICAL
+// ISSUE: KT-51272
+
+import kotlin.reflect.KClass
+
+fun testOnKClass(rootClass: KClass<Any>): Int {
+    return when (rootClass) {
+        Collection::class -> 1
+        else -> 2
+    }
+}
+
+fun testOnClass(rootClass: Class<Any>): Int {
+    return when (rootClass) {
+        Collection::class -> 1
+        else -> 2
+    }
+}
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/callableReference/callableReferenceInWhenExpression.txt b/compiler/testData/diagnostics/tests/callableReference/callableReferenceInWhenExpression.txt
new file mode 100644
index 00000000000..0d180a3a02d
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/callableReference/callableReferenceInWhenExpression.txt
@@ -0,0 +1,4 @@
+package
+
+public fun testOnClass(/*0*/ rootClass: java.lang.Class<kotlin.Any>): kotlin.Int
+public fun testOnKClass(/*0*/ rootClass: kotlin.reflect.KClass<kotlin.Any>): kotlin.Int
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 7f053ffe4fc..b463905f907 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
@@ -2652,6 +2652,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/callableReference/callableReferenceAssignmentToVar.kt");
             }
 
+            @Test
+            @TestMetadata("callableReferenceInWhenExpression.kt")
+            public void testCallableReferenceInWhenExpression() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/callableReference/callableReferenceInWhenExpression.kt");
+            }
+
             @Test
             @TestMetadata("callableReferenceWithMostSpecificGenericTypeParameter.kt")
             public void testCallableReferenceWithMostSpecificGenericTypeParameter() throws Exception {