diff --git a/RegExpSupport/src/org/intellij/lang/regexp/RegExpLanguageHost.java b/RegExpSupport/src/org/intellij/lang/regexp/RegExpLanguageHost.java
index 834332cab4c8..e4c8f5c04fc8 100644
--- a/RegExpSupport/src/org/intellij/lang/regexp/RegExpLanguageHost.java
+++ b/RegExpSupport/src/org/intellij/lang/regexp/RegExpLanguageHost.java
@@ -32,6 +32,16 @@ public interface RegExpLanguageHost {
   boolean supportsNamedGroupRefSyntax(RegExpNamedGroupRef ref);
   boolean supportsExtendedHexCharacter(RegExpChar regExpChar);
 
+  default boolean isValidGroupName(String name, @NotNull PsiElement context) {
+    for (int i = 0, length = name.length(); i < length; i++) {
+      int c = name.codePointAt(i);
+      if (!(c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z' || c >= '0' && c <= '9' || c == '_')) {
+        return false;
+      }
+    }
+    return true;
+  }
+
   default boolean supportsSimpleClass(RegExpSimpleClass simpleClass) {
     return true;
   }
diff --git a/RegExpSupport/src/org/intellij/lang/regexp/RegExpLanguageHosts.java b/RegExpSupport/src/org/intellij/lang/regexp/RegExpLanguageHosts.java
index b76bf14cf5bd..e16fbd5c1143 100644
--- a/RegExpSupport/src/org/intellij/lang/regexp/RegExpLanguageHosts.java
+++ b/RegExpSupport/src/org/intellij/lang/regexp/RegExpLanguageHosts.java
@@ -22,6 +22,7 @@ import com.intellij.psi.PsiComment;
 import com.intellij.psi.PsiElement;
 import com.intellij.psi.PsiLanguageInjectionHost;
 import org.intellij.lang.regexp.psi.*;
+import org.jetbrains.annotations.Contract;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.jetbrains.annotations.TestOnly;
@@ -48,6 +49,7 @@ public final class RegExpLanguageHosts extends ClassExtension<RegExpLanguageHost
     myHost = host;
   }
 
+  @Contract("null -> null")
   @Nullable
   private static RegExpLanguageHost findRegExpHost(@Nullable final PsiElement element) {
     if (ApplicationManager.getApplication().isUnitTestMode() && myHost != null) {
@@ -115,6 +117,11 @@ public final class RegExpLanguageHosts extends ClassExtension<RegExpLanguageHost
     }
   }
 
+  public boolean isValidGroupName(String name, @Nullable final PsiElement context) {
+    final RegExpLanguageHost host = findRegExpHost(context);
+    return host != null && host.isValidGroupName(name, context);
+  }
+
   public boolean supportsPerl5EmbeddedComments(@Nullable final PsiComment comment) {
     final RegExpLanguageHost host = findRegExpHost(comment);
     return host != null && host.supportsPerl5EmbeddedComments();
diff --git a/RegExpSupport/src/org/intellij/lang/regexp/validation/RegExpAnnotator.java b/RegExpSupport/src/org/intellij/lang/regexp/validation/RegExpAnnotator.java
index 905953df927c..f713f6e6e638 100644
--- a/RegExpSupport/src/org/intellij/lang/regexp/validation/RegExpAnnotator.java
+++ b/RegExpSupport/src/org/intellij/lang/regexp/validation/RegExpAnnotator.java
@@ -222,10 +222,7 @@ public final class RegExpAnnotator extends RegExpElementVisitor implements Annot
     }
     if(!myLanguageHosts.isValidCategory(category.getPsi(), category.getText())) {
       final Annotation a = myHolder.createErrorAnnotation(category, "Unknown character category");
-      if (a != null) {
-        // IDEA-9381
-        a.setHighlightType(ProblemHighlightType.LIKE_UNKNOWN_SYMBOL);
-      }
+      a.setHighlightType(ProblemHighlightType.LIKE_UNKNOWN_SYMBOL);
     }
   }
 
@@ -234,10 +231,7 @@ public final class RegExpAnnotator extends RegExpElementVisitor implements Annot
     final RegExpGroup group = backref.resolve();
     if (group == null) {
       final Annotation a = myHolder.createErrorAnnotation(backref, "Unresolved back reference");
-      if (a != null) {
-        // IDEA-9381
-        a.setHighlightType(ProblemHighlightType.LIKE_UNKNOWN_SYMBOL);
-      }
+      a.setHighlightType(ProblemHighlightType.LIKE_UNKNOWN_SYMBOL);
     }
     else if (PsiTreeUtil.isAncestor(group, backref, true)) {
       myHolder.createWarningAnnotation(backref, "Back reference is nested into the capturing group it refers to");
@@ -277,6 +271,11 @@ public final class RegExpAnnotator extends RegExpElementVisitor implements Annot
         myHolder.createErrorAnnotation(group, "This named group syntax is not supported");
       }
     }
+    final String name = group.getName();
+    if (name != null && !myLanguageHosts.isValidGroupName(name, group)) {
+      final ASTNode node = group.getNode().findChildByType(RegExpTT.NAME);
+      if (node != null) myHolder.createErrorAnnotation(node, "Invalid group name");
+    }
   }
 
   @Override
@@ -291,9 +290,8 @@ public final class RegExpAnnotator extends RegExpElementVisitor implements Annot
     final RegExpGroup group = groupRef.resolve();
     if (group == null) {
       final ASTNode node = groupRef.getNode().findChildByType(RegExpTT.NAME);
-      final Annotation a = myHolder.createErrorAnnotation(node, "Unresolved named group reference");
-      if (a != null) {
-        // IDEA-9381
+      if (node != null) {
+        final Annotation a = myHolder.createErrorAnnotation(node, "Unresolved named group reference");
         a.setHighlightType(ProblemHighlightType.LIKE_UNKNOWN_SYMBOL);
       }
     }
@@ -383,9 +381,7 @@ public final class RegExpAnnotator extends RegExpElementVisitor implements Annot
     final String className = posixBracketExpression.getClassName();
     if (!POSIX_CHARACTER_CLASSES.contains(className)) {
       final Annotation annotation = myHolder.createErrorAnnotation(posixBracketExpression, "Unknown POSIX character class");
-      if (annotation != null) {
-        annotation.setHighlightType(ProblemHighlightType.LIKE_UNKNOWN_SYMBOL);
-      }
+      annotation.setHighlightType(ProblemHighlightType.LIKE_UNKNOWN_SYMBOL);
     }
   }
 
diff --git a/RegExpSupport/testData/RETest.xml b/RegExpSupport/testData/RETest.xml
index 02ee29e1f7bf..3e1819f8ace2 100644
--- a/RegExpSupport/testData/RETest.xml
+++ b/RegExpSupport/testData/RETest.xml
@@ -79,6 +79,14 @@
       <pattern><![CDATA[\k<<error descr="Unresolved named group reference">adsf</error>>]]></pattern>
       <expected>OK</expected>
     </test>
+    <test host="com.intellij.psi.impl.JavaRegExpHost" varify="false">
+      <pattern>(?&lt;important_value1&gt;\d\d)</pattern>
+      <expected>ERR</expected>
+    </test>
+    <test host="com.intellij.psi.impl.JavaRegExpHost" varify="false">
+      <pattern>(?&lt;importantValue1&gt;\d\d)</pattern>
+      <expected>OK</expected>
+    </test>
   </groups>
   <escapes>
     <test verify="false">
diff --git a/java/java-impl/src/com/intellij/psi/impl/JavaRegExpHost.java b/java/java-impl/src/com/intellij/psi/impl/JavaRegExpHost.java
index 17e980719fb3..d97a2805883b 100644
--- a/java/java-impl/src/com/intellij/psi/impl/JavaRegExpHost.java
+++ b/java/java-impl/src/com/intellij/psi/impl/JavaRegExpHost.java
@@ -164,6 +164,17 @@ public class JavaRegExpHost implements RegExpLanguageHost {
     return ref.isNamedGroupRef() && hasAtLeastJdkVersion(ref, JavaSdkVersion.JDK_1_7);
   }
 
+  @Override
+  public boolean isValidGroupName(String name, @NotNull PsiElement context) {
+    for (int i = 0, length = name.length(); i < length; i++) {
+      int c = name.codePointAt(i);
+      if (!(c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z' || c >= '0' && c <= '9')) {
+        return false;
+      }
+    }
+    return true;
+  }
+
   @Override
   public boolean supportsExtendedHexCharacter(RegExpChar regExpChar) {
     return hasAtLeastJdkVersion(regExpChar, JavaSdkVersion.JDK_1_7);