diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/testbase/diagnosticsAssertions.kt b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/testbase/diagnosticsAssertions.kt
index 7037df74518..b8723c410d4 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/testbase/diagnosticsAssertions.kt
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/testbase/diagnosticsAssertions.kt
@@ -9,7 +9,6 @@ import org.gradle.testkit.runner.BuildResult
 import org.jetbrains.kotlin.gradle.BaseGradleIT
 import org.jetbrains.kotlin.gradle.internals.VERBOSE_DIAGNOSTIC_SEPARATOR
 import org.jetbrains.kotlin.gradle.plugin.diagnostics.ToolingDiagnosticFactory
-import kotlin.test.assertNotNull
 import kotlin.test.assertNull
 import kotlin.test.assertTrue
 
@@ -17,31 +16,54 @@ fun BaseGradleIT.CompiledProject.assertHasDiagnostic(diagnosticFactory: ToolingD
     output.assertHasDiagnostic(diagnosticFactory, withSubstring)
 }
 
-fun BaseGradleIT.CompiledProject.assertNoDiagnostic(diagnosticFactory: ToolingDiagnosticFactory) {
-    output.assertNoDiagnostic(diagnosticFactory)
+fun BaseGradleIT.CompiledProject.assertNoDiagnostic(diagnosticFactory: ToolingDiagnosticFactory, withSubstring: String? = null) {
+    output.assertNoDiagnostic(diagnosticFactory, withSubstring)
+}
+
+fun BuildResult.assertHasDiagnostic(diagnosticFactory: ToolingDiagnosticFactory, withSubstring: String? = null) {
+    output.assertHasDiagnostic(diagnosticFactory, withSubstring)
+}
+
+fun BuildResult.assertNoDiagnostic(diagnosticFactory: ToolingDiagnosticFactory, withSubstring: String? = null) {
+    output.assertNoDiagnostic(diagnosticFactory, withSubstring)
 }
 
 fun String.assertHasDiagnostic(diagnosticFactory: ToolingDiagnosticFactory, withSubstring: String? = null) {
-    val diagnosticMessage = extractVerboselyRenderedDiagnostic(diagnosticFactory, this)
-    assertNotNull(diagnosticMessage) { "Diagnostic with id=${diagnosticFactory.id} not found" }
+    val diagnosticsMessages = extractVerboselyRenderedDiagnostics(diagnosticFactory, this)
+    assertTrue(diagnosticsMessages.isNotEmpty(), "Diagnostic with id=${diagnosticFactory.id} not found. Full text output:\n\n" + this)
     if (withSubstring != null) {
         assertTrue(
-            withSubstring in diagnosticMessage,
+            diagnosticsMessages.any { withSubstring in it },
             "Diagnostic ${diagnosticFactory.id} doesn't have expected substring $withSubstring. " +
-                    "Actual diagnostic message:\n" +
-                    diagnosticMessage
+                    "Actual diagnostic messages with that ID:\n" +
+                    diagnosticsMessages.joinToString(separator = "\n") +
+                    "\nFull text output:\n\n" +
+                    this
         )
     }
 }
 
-fun String.assertNoDiagnostic(diagnosticFactory: ToolingDiagnosticFactory) {
-    val diagnosticMessage = extractVerboselyRenderedDiagnostic(diagnosticFactory, this)
-    assertNull(
-        diagnosticMessage,
-        "Diagnostic with id=${diagnosticFactory.id} was expected to be absent, but was reported. " +
-                "Actual diagnostic message: \n" +
-                diagnosticMessage
-    )
+fun String.assertNoDiagnostic(diagnosticFactory: ToolingDiagnosticFactory, withSubstring: String? = null) {
+    val diagnosticMessages = extractVerboselyRenderedDiagnostics(diagnosticFactory, this)
+    if (withSubstring != null) {
+        val matchedWithSubstring = diagnosticMessages.find { withSubstring in it }
+        assertNull(
+            matchedWithSubstring,
+            "Diagnostic with id=${diagnosticFactory.id} and substring '${withSubstring}' was expected to be absent, but was reported. " +
+                    "Actual diagnostic message: \n" +
+                    matchedWithSubstring +
+                    "\nFull text output:\n\n" +
+                    this
+        )
+    } else {
+        assertTrue(
+            diagnosticMessages.isEmpty(),
+            "Expected no diagnostics with id=${diagnosticFactory.id}, but some were reported:\n" +
+                    diagnosticMessages.joinToString(separator = "\n") +
+                    "\nFull text output:\n\n" +
+                    this
+        )
+    }
 }
 
 /**
@@ -112,8 +134,23 @@ private val DIAGNOSTIC_START_REGEX = """\s*[we]:\s*\[[^\[]*].*""".toRegex()
      Multiline
          Text"
   */
-private fun extractVerboselyRenderedDiagnostic(diagnostic: ToolingDiagnosticFactory, fromText: String): String? {
-    val diagnosticStartIndex = fromText.indexOf("[${diagnostic.id}")
+private fun extractVerboselyRenderedDiagnostics(diagnostic: ToolingDiagnosticFactory, fromText: String): List<String> {
+    var parsedPrefix = 0
+
+    return generateSequence {
+        extractNextVerboselyRenderedDiagnosticAndIndex(diagnostic, fromText, startIndex = parsedPrefix)
+            ?.also { (_, newPrefix) -> parsedPrefix = newPrefix }
+            ?.first
+    }.toList()
+}
+
+// Returns diagnostic substring + index of the first symbol after the diagnostic message
+private fun extractNextVerboselyRenderedDiagnosticAndIndex(
+    diagnostic: ToolingDiagnosticFactory,
+    fromText: String,
+    startIndex: Int,
+): Pair<String, Int>? {
+    val diagnosticStartIndex = fromText.indexOf("[${diagnostic.id}", startIndex)
     if (diagnosticStartIndex == -1) return null
 
     val diagnosticHeaderEnd = fromText.indexOf("]", startIndex = diagnosticStartIndex)
@@ -121,7 +158,10 @@ private fun extractVerboselyRenderedDiagnostic(diagnostic: ToolingDiagnosticFact
 
     val diagnosticSeparatorStartIndex = fromText.indexOf(VERBOSE_DIAGNOSTIC_SEPARATOR, startIndex = diagnosticStartIndex)
     // NB: substring's endIndex is exclusive, which gives us exactly the message
-    return fromText.substring(diagnosticMessageStart, diagnosticSeparatorStartIndex).trim { it.isWhitespace() || it == '\n' }
+    val diagnosticMessage = fromText.substring(diagnosticMessageStart, diagnosticSeparatorStartIndex)
+        .trim { it.isWhitespace() || it == '\n' }
+    val indexOfFirstSymbolAfterSeparator = diagnosticSeparatorStartIndex + VERBOSE_DIAGNOSTIC_SEPARATOR.length
+    return diagnosticMessage to indexOfFirstSymbolAfterSeparator
 }
 
 private const val CONFIGURE_PROJECT_PREFIX = "> Configure project"
diff --git a/libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/diagnostics/renderReportedDiagnostics.kt b/libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/diagnostics/renderReportedDiagnostics.kt
index 7ec351f70df..6220dde6b1c 100644
--- a/libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/diagnostics/renderReportedDiagnostics.kt
+++ b/libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/diagnostics/renderReportedDiagnostics.kt
@@ -5,6 +5,7 @@
 
 package org.jetbrains.kotlin.gradle.plugin.diagnostics
 
+import org.gradle.api.InvalidUserCodeException
 import org.gradle.api.logging.Logger
 import org.jetbrains.kotlin.gradle.plugin.diagnostics.ToolingDiagnostic.Severity.*
 
@@ -24,8 +25,7 @@ internal fun renderReportedDiagnostic(
 
         ERROR -> logger.error("e: ${diagnostic.render(isVerbose)}\n")
 
-        FATAL ->
-            error("Internal error: FATAL diagnostics throw an exception immediately in KotlinToolingDiagnosticsCollector")
+        FATAL -> throw InvalidUserCodeException(diagnostic.render(isVerbose))
     }
 }