diff --git a/compiler/frontend/src/org/jetbrains/kotlin/idea/MainFunctionDetector.kt b/compiler/frontend/src/org/jetbrains/kotlin/idea/MainFunctionDetector.kt
index 7916fc118a3..b10a03c598c 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/idea/MainFunctionDetector.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/idea/MainFunctionDetector.kt
@@ -30,6 +30,7 @@ import org.jetbrains.kotlin.resolve.annotations.hasJvmStaticAnnotation
 import org.jetbrains.kotlin.resolve.descriptorUtil.module
 import org.jetbrains.kotlin.resolve.scopes.MemberScope
 import org.jetbrains.kotlin.types.Variance
+import org.jetbrains.kotlin.utils.KotlinExceptionWithAttachments
 
 class MainFunctionDetector {
     private val getFunctionDescriptor: (KtNamedFunction) -> FunctionDescriptor?
@@ -39,7 +40,8 @@ class MainFunctionDetector {
     constructor(bindingContext: BindingContext, languageVersionSettings: LanguageVersionSettings) {
         this.getFunctionDescriptor = { function ->
             bindingContext.get(BindingContext.FUNCTION, function)
-                ?: throw IllegalStateException("No descriptor resolved for " + function + " " + function.text)
+                ?: throw throw KotlinExceptionWithAttachments("No descriptor resolved for $function")
+                    .withAttachment("function.text", function.text)
         }
         this.languageVersionSettings = languageVersionSettings
     }
diff --git a/idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/ToFromOriginalFileMapper.kt b/idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/ToFromOriginalFileMapper.kt
index a009cc73d58..6dcf81e2361 100644
--- a/idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/ToFromOriginalFileMapper.kt
+++ b/idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/ToFromOriginalFileMapper.kt
@@ -21,6 +21,7 @@ import com.intellij.psi.PsiElement
 import com.intellij.psi.util.PsiTreeUtil
 import org.jetbrains.kotlin.psi.KtFile
 import org.jetbrains.kotlin.psi.psiUtil.startOffset
+import org.jetbrains.kotlin.utils.KotlinExceptionWithAttachments
 import kotlin.math.min
 
 class ToFromOriginalFileMapper private constructor(
@@ -46,7 +47,16 @@ class ToFromOriginalFileMapper private constructor(
     init {
         val originalText = originalFile.text
         val syntheticText = syntheticFile.text
-        assert(originalText.subSequence(0, completionOffset) == syntheticText.subSequence(0, completionOffset))
+        val originalSubSequence = originalText.subSequence(0, completionOffset)
+        val syntheticSubSequence = syntheticText.subSequence(0, completionOffset)
+        if (originalSubSequence != syntheticSubSequence) {
+            throw KotlinExceptionWithAttachments(
+                "original subText [len: ${originalSubSequence.length}]" +
+                        " does not match synthetic subText [len: ${syntheticSubSequence.length}]"
+            )
+                .withAttachment("original subText", originalSubSequence.toString())
+                .withAttachment("synthetic subText", syntheticSubSequence.toString())
+        }
 
         syntheticLength = syntheticText.length
         originalLength = originalText.length