diff --git a/CHANGES.txt b/CHANGES.txt
index 4878986eb..0bb867b98 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -3,6 +3,7 @@ ANTLR v4 Honey Badger
 November 17, 2012
 
 * .tokens files goes in output dir like parser file.
+* added check: action in lexer rules must be last element of outermost alt
 
 November 11, 2012
 
diff --git a/tool/playground/T.g b/tool/playground/T.g
index 86969ed2e..ba5a58d69 100644
--- a/tool/playground/T.g
+++ b/tool/playground/T.g
@@ -1,8 +1,8 @@
 grammar T;
-s : ~(ID|X)* X ;
-b : ~(ID|X)*? X ;
-A : 'a' ;
-B : 'b' ;
-X : 'x' ;
-ID : 'id' ;
+s : A ;
+
+A : {} 'a' ;
+
+B : ('x' {}|{}'y') {} ;
+
 WS : [ \t\r\n]+ -> skip ;
diff --git a/tool/src/org/antlr/v4/semantics/BasicSemanticChecks.java b/tool/src/org/antlr/v4/semantics/BasicSemanticChecks.java
index 6a7641bf8..9efec92ec 100644
--- a/tool/src/org/antlr/v4/semantics/BasicSemanticChecks.java
+++ b/tool/src/org/antlr/v4/semantics/BasicSemanticChecks.java
@@ -30,6 +30,8 @@
 package org.antlr.v4.semantics;
 
 import org.antlr.runtime.Token;
+import org.antlr.runtime.tree.CommonTree;
+import org.antlr.runtime.tree.Tree;
 import org.antlr.v4.misc.Utils;
 import org.antlr.v4.parse.ANTLRParser;
 import org.antlr.v4.parse.GrammarTreeVisitor;
@@ -322,6 +324,28 @@ public class BasicSemanticChecks extends GrammarTreeVisitor {
 		}
 	}
 
+	@Override
+	protected void enterLexerElement(GrammarAST tree) {
+		if ( tree.getType() == ACTION ) {
+			// Make sure that action is last element in outer alt; here action
+			// and a2 are bad, but a3 is ok.
+			// (RULE A (BLOCK (ALT {action} 'a')))
+			// (RULE B (BLOCK (ALT (BLOCK (ALT {a2} 'x') (ALT 'y')) {a3})))
+			CommonTree alt = tree.parent;
+			CommonTree blk = alt.parent;
+			boolean outerMostAlt = blk.parent.getType() != RULE;
+			Tree rule = tree.getAncestor(RULE);
+			String fileName = tree.getToken().getInputStream().getSourceName();
+			if ( !outerMostAlt || tree.getChildIndex() != alt.getChildCount()-1 ) {
+				g.tool.errMgr.grammarError(ErrorType.LEXER_ACTION_PLACEMENT_ISSUE,
+										   fileName,
+										   tree.getToken(),
+										   rule.getChild(0).getText());
+
+			}
+		}
+	}
+
 	@Override
 	public void label(GrammarAST op, GrammarAST ID, GrammarAST element) {
 		switch (element.getType()) {
diff --git a/tool/src/org/antlr/v4/tool/ErrorType.java b/tool/src/org/antlr/v4/tool/ErrorType.java
index 2988023a4..4f1aa2bd9 100644
--- a/tool/src/org/antlr/v4/tool/ErrorType.java
+++ b/tool/src/org/antlr/v4/tool/ErrorType.java
@@ -153,6 +153,7 @@ public enum ErrorType {
 //	WILDCARD_IN_PARSER(129, "wildcard '.' not allowed in parsers", ErrorSeverity.ERROR),
 	LABEL_BLOCK_NOT_A_SET(130, "label <arg> assigned to a block which is not a set", ErrorSeverity.ERROR),
 	EXPECTED_NON_GREEDY_WILDCARD_BLOCK(131, "greedy block ()<arg> contains wildcard; the non-greedy syntax ()<arg>? may be preferred", ErrorSeverity.WARNING),
+	LEXER_ACTION_PLACEMENT_ISSUE(132, "action in lexer rule <arg> must be last element of outermost alt", ErrorSeverity.ERROR),
 
 	/** Documentation comment is unterminated */
     //UNTERMINATED_DOC_COMMENT(, "", ErrorSeverity.ERROR),