diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirOptInUsageBaseChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirOptInUsageBaseChecker.kt
index deb049328b1..73ceb2334cf 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirOptInUsageBaseChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirOptInUsageBaseChecker.kt
@@ -238,7 +238,7 @@ object FirOptInUsageBaseChecker {
                 }
                 val fqName = annotationClassId.asSingleFqName()
                 val reportedMessage = message?.takeIf { it.isNotBlank() }
-                    ?: OptInNames.buildDefaultDiagnosticMessage(OptInNames.buildMessagePrefix(verb), fqName)
+                    ?: OptInNames.buildDefaultDiagnosticMessage(OptInNames.buildMessagePrefix(verb), fqName.asString())
                 reporter.reportOn(element.source, diagnostic, fqName, reportedMessage, context)
             }
         }
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/ExperimentalUsageChecker.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/ExperimentalUsageChecker.kt
index 4a3c90f5108..1b389863c6e 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/ExperimentalUsageChecker.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/ExperimentalUsageChecker.kt
@@ -119,7 +119,7 @@ class ExperimentalUsageChecker(project: Project) : CallChecker {
         private val ERROR_LEVEL = Name.identifier("ERROR")
 
         internal fun getDefaultDiagnosticMessage(prefix: String): (FqName) -> String = { fqName: FqName ->
-            OptInNames.buildDefaultDiagnosticMessage(prefix, fqName)
+            OptInNames.buildDefaultDiagnosticMessage(prefix, fqName.asString())
         }
 
         private val USAGE_DIAGNOSTICS = ExperimentalityDiagnostics(
diff --git a/compiler/testData/cli/jvm/optInEmptyMessage.out b/compiler/testData/cli/jvm/optInEmptyMessage.out
index 168a6ceb01f..6154ea01794 100644
--- a/compiler/testData/cli/jvm/optInEmptyMessage.out
+++ b/compiler/testData/cli/jvm/optInEmptyMessage.out
@@ -1,4 +1,4 @@
-compiler/testData/cli/jvm/optInEmptyMessage.kt:8:5: error: this declaration needs OptIn. Its usage must be marked with '@EmptyMarker' or '@OptIn(EmptyMarker::class)'
+compiler/testData/cli/jvm/optInEmptyMessage.kt:8:5: error: this declaration needs opt-in. Its usage must be marked with '@EmptyMarker' or '@OptIn(EmptyMarker::class)'
     foo()
     ^
 COMPILATION_ERROR
diff --git a/compiler/testData/cli/jvm/optInEmptyMessageFir.out b/compiler/testData/cli/jvm/optInEmptyMessageFir.out
index 93e72cd154c..56de940031f 100644
--- a/compiler/testData/cli/jvm/optInEmptyMessageFir.out
+++ b/compiler/testData/cli/jvm/optInEmptyMessageFir.out
@@ -1,7 +1,7 @@
 warning: ATTENTION!
  This build uses in-dev FIR:
   -Xuse-fir
-compiler/testData/cli/jvm/optInEmptyMessageFir.kt:8:5: error: this declaration needs OptIn. Its usage must be marked with '@EmptyMarker' or '@OptIn(EmptyMarker::class)'
+compiler/testData/cli/jvm/optInEmptyMessageFir.kt:8:5: error: this declaration needs opt-in. Its usage must be marked with '@EmptyMarker' or '@OptIn(EmptyMarker::class)'
     foo()
     ^
 COMPILATION_ERROR
diff --git a/compiler/testData/cli/jvm/optInOverrideMessage.out b/compiler/testData/cli/jvm/optInOverrideMessage.out
index 78c82f2c1ff..4d4631f8618 100644
--- a/compiler/testData/cli/jvm/optInOverrideMessage.out
+++ b/compiler/testData/cli/jvm/optInOverrideMessage.out
@@ -1,7 +1,7 @@
-compiler/testData/cli/jvm/optInOverrideMessage.kt:16:18: error: base declaration of supertype 'Base' needs OptIn. This API is experimental and can change at any time, please use with care. The declaration override must be annotated with '@Marker'
+compiler/testData/cli/jvm/optInOverrideMessage.kt:16:18: error: base declaration of supertype 'Base' needs opt-in. This API is experimental and can change at any time, please use with care. The declaration override must be annotated with '@Marker' or '@OptIn(Marker::class)'
     override fun foo() {}
                  ^
-compiler/testData/cli/jvm/optInOverrideMessage.kt:18:18: error: base declaration of supertype 'Base' needs OptIn. The declaration override must be annotated with '@EmptyMarker'
+compiler/testData/cli/jvm/optInOverrideMessage.kt:18:18: error: base declaration of supertype 'Base' needs opt-in. The declaration override must be annotated with '@EmptyMarker' or '@OptIn(EmptyMarker::class)'
     override fun bar() {}
                  ^
 COMPILATION_ERROR
diff --git a/compiler/testData/cli/jvm/optInOverrideMessageFir.out b/compiler/testData/cli/jvm/optInOverrideMessageFir.out
index 54278f08d8e..47f7dc82ff1 100644
--- a/compiler/testData/cli/jvm/optInOverrideMessageFir.out
+++ b/compiler/testData/cli/jvm/optInOverrideMessageFir.out
@@ -1,10 +1,10 @@
 warning: ATTENTION!
  This build uses in-dev FIR:
   -Xuse-fir
-compiler/testData/cli/jvm/optInOverrideMessageFir.kt:16:18: error: base declaration of supertype 'Base' needs OptIn. This API is experimental and can change at any time, please use with care. The declaration override must be annotated with '@Marker'
+compiler/testData/cli/jvm/optInOverrideMessageFir.kt:16:18: error: base declaration of supertype 'Base' needs opt-in. This API is experimental and can change at any time, please use with care. The declaration override must be annotated with '@Marker' or '@OptIn(Marker::class)'
     override fun foo() {}
                  ^
-compiler/testData/cli/jvm/optInOverrideMessageFir.kt:18:18: error: base declaration of supertype 'Base' needs OptIn. The declaration override must be annotated with '@EmptyMarker'
+compiler/testData/cli/jvm/optInOverrideMessageFir.kt:18:18: error: base declaration of supertype 'Base' needs opt-in. The declaration override must be annotated with '@EmptyMarker' or '@OptIn(EmptyMarker::class)'
     override fun bar() {}
                  ^
 COMPILATION_ERROR
diff --git a/compiler/testData/cli/jvm/useDeclarationThatWasExperimentalWithoutMarker2.out b/compiler/testData/cli/jvm/useDeclarationThatWasExperimentalWithoutMarker2.out
index d96ed48710c..e982387af1f 100644
--- a/compiler/testData/cli/jvm/useDeclarationThatWasExperimentalWithoutMarker2.out
+++ b/compiler/testData/cli/jvm/useDeclarationThatWasExperimentalWithoutMarker2.out
@@ -1,17 +1,17 @@
 warning: language version 1.4 is deprecated and its support will be removed in a future version of Kotlin
-compiler/testData/cli/jvm/useDeclarationThatWasExperimentalWithoutMarker2.kt:2:13: warning: this declaration needs OptIn. Its usage should be marked with '@kotlin.ExperimentalUnsignedTypes' or '@OptIn(kotlin.ExperimentalUnsignedTypes::class)'
+compiler/testData/cli/jvm/useDeclarationThatWasExperimentalWithoutMarker2.kt:2:13: warning: this declaration needs opt-in. Its usage should be marked with '@kotlin.ExperimentalUnsignedTypes' or '@OptIn(kotlin.ExperimentalUnsignedTypes::class)'
 fun test(p: ULong) {
             ^
-compiler/testData/cli/jvm/useDeclarationThatWasExperimentalWithoutMarker2.kt:3:12: warning: this declaration needs OptIn. Its usage should be marked with '@kotlin.ExperimentalUnsignedTypes' or '@OptIn(kotlin.ExperimentalUnsignedTypes::class)'
+compiler/testData/cli/jvm/useDeclarationThatWasExperimentalWithoutMarker2.kt:3:12: warning: this declaration needs opt-in. Its usage should be marked with '@kotlin.ExperimentalUnsignedTypes' or '@OptIn(kotlin.ExperimentalUnsignedTypes::class)'
     val z: ULong = p
            ^
-compiler/testData/cli/jvm/useDeclarationThatWasExperimentalWithoutMarker2.kt:3:20: warning: this declaration needs OptIn. Its usage should be marked with '@kotlin.ExperimentalUnsignedTypes' or '@OptIn(kotlin.ExperimentalUnsignedTypes::class)'
+compiler/testData/cli/jvm/useDeclarationThatWasExperimentalWithoutMarker2.kt:3:20: warning: this declaration needs opt-in. Its usage should be marked with '@kotlin.ExperimentalUnsignedTypes' or '@OptIn(kotlin.ExperimentalUnsignedTypes::class)'
     val z: ULong = p
                    ^
-compiler/testData/cli/jvm/useDeclarationThatWasExperimentalWithoutMarker2.kt:4:5: warning: this declaration needs OptIn. Its usage should be marked with '@kotlin.ExperimentalUnsignedTypes' or '@OptIn(kotlin.ExperimentalUnsignedTypes::class)'
+compiler/testData/cli/jvm/useDeclarationThatWasExperimentalWithoutMarker2.kt:4:5: warning: this declaration needs opt-in. Its usage should be marked with '@kotlin.ExperimentalUnsignedTypes' or '@OptIn(kotlin.ExperimentalUnsignedTypes::class)'
     z.inv()
     ^
-compiler/testData/cli/jvm/useDeclarationThatWasExperimentalWithoutMarker2.kt:4:7: warning: this declaration needs OptIn. Its usage should be marked with '@kotlin.ExperimentalUnsignedTypes' or '@OptIn(kotlin.ExperimentalUnsignedTypes::class)'
+compiler/testData/cli/jvm/useDeclarationThatWasExperimentalWithoutMarker2.kt:4:7: warning: this declaration needs opt-in. Its usage should be marked with '@kotlin.ExperimentalUnsignedTypes' or '@OptIn(kotlin.ExperimentalUnsignedTypes::class)'
     z.inv()
       ^
 OK
diff --git a/core/compiler.common/src/org/jetbrains/kotlin/resolve/checkers/OptInNames.kt b/core/compiler.common/src/org/jetbrains/kotlin/resolve/checkers/OptInNames.kt
index cb15382d821..181fc4b8f1d 100644
--- a/core/compiler.common/src/org/jetbrains/kotlin/resolve/checkers/OptInNames.kt
+++ b/core/compiler.common/src/org/jetbrains/kotlin/resolve/checkers/OptInNames.kt
@@ -39,18 +39,18 @@ object OptInNames {
     @Suppress("unused")
     val USE_EXPERIMENTAL_FQ_NAMES = OPT_IN_FQ_NAMES
 
-    fun buildDefaultDiagnosticMessage(prefix: String, fqName: FqName): String {
-        return "$prefix with '@${fqName.asString()}' or '@OptIn(${fqName.asString()}::class)'"
+    fun buildDefaultDiagnosticMessage(prefix: String, markerName: String): String {
+        return "$prefix with '@$markerName' or '@OptIn($markerName::class)'"
     }
 
     fun buildMessagePrefix(verb: String): String =
-        "This declaration needs OptIn. Its usage $verb be marked"
+        "This declaration needs opt-in. Its usage $verb be marked"
 
     fun buildOverrideMessage(supertypeName: String, markerMessage: String?, verb: String, markerName: String): String {
-        val basePrefix = "Base declaration of supertype '$supertypeName' needs OptIn. "
+        val basePrefix = "Base declaration of supertype '$supertypeName' needs opt-in. "
         val markerMessageOrStub = markerMessage
             ?.takeIf { it.isNotBlank() }?.let { if (it.endsWith(".")) "$it " else "$it. " } ?: ""
-        val baseSuffix = "The declaration override $verb be annotated with '@$markerName'"
+        val baseSuffix = buildDefaultDiagnosticMessage("The declaration override $verb be annotated", markerName)
         return basePrefix + markerMessageOrStub + baseSuffix
     }
 }
\ No newline at end of file