diff --git a/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostics/DiagnosticsCollector.kt b/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostics/DiagnosticsCollector.kt
index 0454487c65c..4f9741585d0 100644
--- a/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostics/DiagnosticsCollector.kt
+++ b/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostics/DiagnosticsCollector.kt
@@ -20,7 +20,7 @@ internal class DiagnosticsCollector(private val fileStructureCache: FileStructur
         return diagnostics.diagnosticsFor(filter, element)
     }
 
-    fun collectDiagnosticsForFile(ktFile: KtFile, filter: DiagnosticCheckerFilter): Collection<KtPsiDiagnostic> {
+    fun collectDiagnosticsForFile(ktFile: KtFile, filter: DiagnosticCheckerFilter): List<KtPsiDiagnostic> {
         val fileStructure = fileStructureCache.getFileStructure(ktFile)
         return fileStructure.getAllDiagnosticsForFile(filter)
     }
diff --git a/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/file/structure/FileStructure.kt b/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/file/structure/FileStructure.kt
index 0f94f07af18..786010f4261 100644
--- a/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/file/structure/FileStructure.kt
+++ b/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/file/structure/FileStructure.kt
@@ -113,7 +113,7 @@ internal class FileStructure private constructor(
         return false
     }
 
-    fun getAllDiagnosticsForFile(diagnosticCheckerFilter: DiagnosticCheckerFilter): Collection<KtPsiDiagnostic> {
+    fun getAllDiagnosticsForFile(diagnosticCheckerFilter: DiagnosticCheckerFilter): List<KtPsiDiagnostic> {
         // TODO, KT-60799: Add a new FileStructure for file diagnostics
         firFile.lazyResolveToPhase(FirResolvePhase.BODY_RESOLVE)
         val structureElements = getAllStructureElements()