diff --git a/Changelog.md b/Changelog.md
index a665eb576..954518dc5 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -22,6 +22,7 @@ Compiler Features:
 
 
 Bugfixes:
+ * Parser: Disallow several ``indexed`` attributes for the same event parameter.
  * Yul Optimizer: Hash hex and decimal literals according to their value instead of their representation, improving the detection of equivalent functions.
  * Solidity Upgrade Tool ``solidity-upgrade``: Fix the tool returning success code on uncaught exceptions.
  * SMTChecker: Fix display error for negative integers that are one more than powers of two.
diff --git a/libsolidity/parsing/Parser.cpp b/libsolidity/parsing/Parser.cpp
index fee21e518..e028b13ac 100644
--- a/libsolidity/parsing/Parser.cpp
+++ b/libsolidity/parsing/Parser.cpp
@@ -785,7 +785,12 @@ ASTPointer<VariableDeclaration> Parser::parseVariableDeclaration(
 		else
 		{
 			if (_options.allowIndexed && token == Token::Indexed)
+			{
+				if (isIndexed)
+					parserError(5399_error, "Indexed already specified.");
+
 				isIndexed = true;
+			}
 			else if (token == Token::Constant || token == Token::Immutable)
 			{
 				if (mutability != VariableDeclaration::Mutability::Mutable)
diff --git a/test/libsolidity/syntaxTests/events/event_several_indexed_of_one_parameter.sol b/test/libsolidity/syntaxTests/events/event_several_indexed_of_one_parameter.sol
new file mode 100644
index 000000000..dd6edd825
--- /dev/null
+++ b/test/libsolidity/syntaxTests/events/event_several_indexed_of_one_parameter.sol
@@ -0,0 +1,9 @@
+contract c {
+    event e(uint indexed a, bytes3 indexed indexed s, bool indexed indexed indexed b);
+    event e2(uint indexed indexed a, bytes3 indexed s);
+}
+// ----
+// ParserError 5399: (56-63): Indexed already specified.
+// ParserError 5399: (80-87): Indexed already specified.
+// ParserError 5399: (88-95): Indexed already specified.
+// ParserError 5399: (126-133): Indexed already specified.