diff --git a/java/java-impl/src/com/intellij/codeInsight/completion/commands/core/CommandCompletionProvider.kt b/java/java-impl/src/com/intellij/codeInsight/completion/commands/core/CommandCompletionProvider.kt
index ab53792153a4..63801355b3a2 100644
--- a/java/java-impl/src/com/intellij/codeInsight/completion/commands/core/CommandCompletionProvider.kt
+++ b/java/java-impl/src/com/intellij/codeInsight/completion/commands/core/CommandCompletionProvider.kt
@@ -2,8 +2,8 @@
 package com.intellij.codeInsight.completion.commands.core
 
 import com.intellij.codeInsight.completion.*
-import com.intellij.codeInsight.completion.commands.api.CompletionCommand
 import com.intellij.codeInsight.completion.commands.api.CommandCompletionFactory
+import com.intellij.codeInsight.completion.commands.api.CompletionCommand
 import com.intellij.codeInsight.completion.impl.CamelHumpMatcher
 import com.intellij.codeInsight.completion.ml.MLWeigherUtil
 import com.intellij.codeInsight.lookup.LookupElement
@@ -23,7 +23,6 @@ import com.intellij.openapi.util.registry.Registry
 import com.intellij.openapi.util.text.StringUtil
 import com.intellij.patterns.PatternCondition
 import com.intellij.patterns.StandardPatterns
-import com.intellij.psi.PsiDocumentManager
 import com.intellij.psi.PsiFile
 import com.intellij.psi.PsiFileFactory
 import com.intellij.testFramework.LightVirtualFile
@@ -43,7 +42,7 @@ internal class CommandCompletionProvider : CompletionProvider<CompletionParamete
     context: ProcessingContext,
     resultSet: CompletionResultSet,
   ) {
-    if(!Registry.`is`("java.completion.command.enabled")) return
+    if (!Registry.`is`("java.completion.command.enabled")) return
     resultSet.runRemainingContributors(parameters) {
       resultSet.passResult(it)
     }
@@ -230,7 +229,7 @@ internal sealed interface InvocationCommandType {
 internal fun findActualIndex(suffix: String, text: CharSequence, offset: Int): Int {
   var indexOf = suffix.length
   if (offset > text.length || offset == 0) return 0
-  while (indexOf > 0 && text.substring(offset - indexOf, offset) != suffix.substring(0, indexOf)) {
+  while (indexOf > 0 && offset - indexOf >= 0 && text.substring(offset - indexOf, offset) != suffix.substring(0, indexOf)) {
     indexOf--
   }
   //try to find outside
diff --git a/java/java-impl/src/com/intellij/codeInsight/completion/commands/core/CommandCompletionService.kt b/java/java-impl/src/com/intellij/codeInsight/completion/commands/core/CommandCompletionService.kt
index 94151532224c..212d3cc7d36f 100644
--- a/java/java-impl/src/com/intellij/codeInsight/completion/commands/core/CommandCompletionService.kt
+++ b/java/java-impl/src/com/intellij/codeInsight/completion/commands/core/CommandCompletionService.kt
@@ -78,9 +78,13 @@ class CommandCompletionService(
     val language = lookup.psiFile?.language ?: return
     val completionFactory = getFactory(language)
     val filterSuffix = completionFactory?.filterSuffix() ?: return
-    val index = findActualIndex(completionFactory.suffix() + filterSuffix.toString(), lookup.editor.document.immutableCharSequence, lookup.lookupOriginalStart)
+    val fullSuffix = completionFactory.suffix() + filterSuffix.toString()
+    val index = findActualIndex(fullSuffix, lookup.editor.document.immutableCharSequence, lookup.lookupOriginalStart)
     if (index == 0) return
-    if (lookup.lookupOriginalStart - index + 1 < lookup.editor.document.textLength && lookup.editor.document.immutableCharSequence[lookup.lookupOriginalStart - index + 1] != filterSuffix) return
+    val offsetOfFullIndex = lookup.lookupOriginalStart - index
+    if (offsetOfFullIndex < 0 ||
+        offsetOfFullIndex >= lookup.editor.document.textLength ||
+        lookup.editor.document.immutableCharSequence.substring(offsetOfFullIndex) != fullSuffix) return
     lookup.putUserData(INSTALLED_ADDITIONAL_MATCHER_KEY, true)
     lookup.arranger.registerAdditionalMatcher(CommandCompletionLookupItemFilter)
     lookup.arranger.prefixChanged(lookup);