diff --git a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java
index b3ecbc597fc..5695dae87ab 100644
--- a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java
+++ b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java
@@ -10570,6 +10570,12 @@ public class DiagnosticCompilerTestFE10TestdataTestGenerated extends AbstractDia
                 runTest("compiler/testData/diagnostics/tests/delegatedProperty/useTypeParameterOfExtensionProperty2.kt");
             }
 
+            @Test
+            @TestMetadata("useTypeParameterOfExtensionProperty3.kt")
+            public void testUseTypeParameterOfExtensionProperty3() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/delegatedProperty/useTypeParameterOfExtensionProperty3.kt");
+            }
+
             @Test
             @TestMetadata("useTypeParameterOfExtensionProperty_Disabled.kt")
             public void testUseTypeParameterOfExtensionProperty_Disabled() throws Exception {
diff --git a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java
index 148bbdcdfd6..122263f7a85 100644
--- a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java
+++ b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java
@@ -10570,6 +10570,12 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated
                 runTest("compiler/testData/diagnostics/tests/delegatedProperty/useTypeParameterOfExtensionProperty2.kt");
             }
 
+            @Test
+            @TestMetadata("useTypeParameterOfExtensionProperty3.kt")
+            public void testUseTypeParameterOfExtensionProperty3() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/delegatedProperty/useTypeParameterOfExtensionProperty3.kt");
+            }
+
             @Test
             @TestMetadata("useTypeParameterOfExtensionProperty_Disabled.kt")
             public void testUseTypeParameterOfExtensionProperty_Disabled() throws Exception {
diff --git a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java
index 5ef4ce9ddc3..c53285e7a44 100644
--- a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java
+++ b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java
@@ -10564,6 +10564,12 @@ public class FirLightTreeOldFrontendDiagnosticsTestGenerated extends AbstractFir
                 runTest("compiler/testData/diagnostics/tests/delegatedProperty/useTypeParameterOfExtensionProperty2.kt");
             }
 
+            @Test
+            @TestMetadata("useTypeParameterOfExtensionProperty3.kt")
+            public void testUseTypeParameterOfExtensionProperty3() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/delegatedProperty/useTypeParameterOfExtensionProperty3.kt");
+            }
+
             @Test
             @TestMetadata("useTypeParameterOfExtensionProperty_Disabled.kt")
             public void testUseTypeParameterOfExtensionProperty_Disabled() throws Exception {
diff --git a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java
index a1933493da2..fa5116a8acc 100644
--- a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java
+++ b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java
@@ -10570,6 +10570,12 @@ public class FirPsiOldFrontendDiagnosticsTestGenerated extends AbstractFirPsiDia
                 runTest("compiler/testData/diagnostics/tests/delegatedProperty/useTypeParameterOfExtensionProperty2.kt");
             }
 
+            @Test
+            @TestMetadata("useTypeParameterOfExtensionProperty3.kt")
+            public void testUseTypeParameterOfExtensionProperty3() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/delegatedProperty/useTypeParameterOfExtensionProperty3.kt");
+            }
+
             @Test
             @TestMetadata("useTypeParameterOfExtensionProperty_Disabled.kt")
             public void testUseTypeParameterOfExtensionProperty_Disabled() throws Exception {
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirDelegateUsesExtensionPropertyTypeParameterChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirDelegateUsesExtensionPropertyTypeParameterChecker.kt
index 175bae16445..8022e64d41d 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirDelegateUsesExtensionPropertyTypeParameterChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirDelegateUsesExtensionPropertyTypeParameterChecker.kt
@@ -12,17 +12,19 @@ import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.checkers.unsubstitutedScope
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
 import org.jetbrains.kotlin.fir.declarations.FirProperty
-import org.jetbrains.kotlin.fir.expressions.FirFunctionCall
+import org.jetbrains.kotlin.fir.declarations.utils.isExtension
+import org.jetbrains.kotlin.fir.expressions.FirExpression
 import org.jetbrains.kotlin.fir.resolve.fullyExpandedType
 import org.jetbrains.kotlin.fir.resolve.toSymbol
 import org.jetbrains.kotlin.fir.scopes.processAllProperties
-import org.jetbrains.kotlin.fir.symbols.impl.FirRegularClassSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirClassSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
 import org.jetbrains.kotlin.fir.types.*
 
 object FirDelegateUsesExtensionPropertyTypeParameterChecker : FirPropertyChecker(MppCheckerKind.Common) {
     override fun check(declaration: FirProperty, context: CheckerContext, reporter: DiagnosticReporter) {
-        val delegate = declaration.delegate as? FirFunctionCall ?: return
+        if (!declaration.isExtension) return
+        val delegate = declaration.delegate ?: return
         val parameters = declaration.typeParameters.mapTo(hashSetOf()) { it.symbol }
 
         val usedTypeParameterSymbol = delegate.resolvedType.findUsedTypeParameterSymbol(parameters, delegate, context, reporter)
@@ -33,14 +35,14 @@ object FirDelegateUsesExtensionPropertyTypeParameterChecker : FirPropertyChecker
 
     private fun ConeKotlinType.findUsedTypeParameterSymbol(
         typeParameterSymbols: HashSet<FirTypeParameterSymbol>,
-        delegate: FirFunctionCall,
+        delegate: FirExpression,
         context: CheckerContext,
         reporter: DiagnosticReporter,
     ): FirTypeParameterSymbol? {
         val expandedDelegateClassLikeType =
             delegate.resolvedType.lowerBoundIfFlexible().fullyExpandedType(context.session)
                 .unwrapDefinitelyNotNull() as? ConeClassLikeType ?: return null
-        val delegateClassSymbol = expandedDelegateClassLikeType.lookupTag.toSymbol(context.session) as? FirRegularClassSymbol ?: return null
+        val delegateClassSymbol = expandedDelegateClassLikeType.lookupTag.toSymbol(context.session) as? FirClassSymbol<*> ?: return null
         val delegateClassScope by lazy { delegateClassSymbol.unsubstitutedScope(context) }
         for (it in typeArguments) {
             val theType = it.type ?: continue
diff --git a/compiler/testData/diagnostics/tests/delegatedProperty/useTypeParameterOfExtensionProperty3.kt b/compiler/testData/diagnostics/tests/delegatedProperty/useTypeParameterOfExtensionProperty3.kt
new file mode 100644
index 00000000000..d0d148fe8e5
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/delegatedProperty/useTypeParameterOfExtensionProperty3.kt
@@ -0,0 +1,23 @@
+// FIR_IDENTICAL
+// ISSUE: KT-64102
+// !DIAGNOSTICS: -DEBUG_INFO_SMARTCAST
+// !LANGUAGE: +ForbidUsingExtensionPropertyTypeParameterInDelegate
+// WITH_REFLECT
+
+import kotlin.reflect.KProperty
+
+class Inv<T>(var t: T)
+
+open class Delegate<X> {
+    var x: X? = null
+    operator fun getValue(thisRef: Inv<X>, property: KProperty<*>) {
+        val _x = x
+        if (_x != null) {
+            thisRef.t = _x
+        } else {
+            x = thisRef.t
+        }
+    }
+}
+
+val <T> Inv<T>.x: Unit <!DELEGATE_USES_EXTENSION_PROPERTY_TYPE_PARAMETER_ERROR!>by object : Delegate<T>() {}<!>
\ No newline at end of file
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 0dcd1fb5933..23ae7c38954 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
@@ -10570,6 +10570,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/delegatedProperty/useTypeParameterOfExtensionProperty2.kt");
             }
 
+            @Test
+            @TestMetadata("useTypeParameterOfExtensionProperty3.kt")
+            public void testUseTypeParameterOfExtensionProperty3() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/delegatedProperty/useTypeParameterOfExtensionProperty3.kt");
+            }
+
             @Test
             @TestMetadata("useTypeParameterOfExtensionProperty_Disabled.kt")
             public void testUseTypeParameterOfExtensionProperty_Disabled() throws Exception {