diff --git a/include/swift/AST/DiagnosticsParse.def b/include/swift/AST/DiagnosticsParse.def
index bb75f58ee9879..7bc1a2e8592ac 100644
--- a/include/swift/AST/DiagnosticsParse.def
+++ b/include/swift/AST/DiagnosticsParse.def
@@ -2178,8 +2178,8 @@ ERROR(expected_lparen_after_lifetime_dependence, PointsToFirstBadToken,
 
 ERROR(expected_identifier_or_index_or_self_after_lifetime_dependence,
       PointsToFirstBadToken,
-      "expected 'copy', 'borrow', or '&' followed by an identifier, index or 'self' in lifetime dependence specifier",
-      ())
+      "expected 'copy', 'borrow', or '&' followed by an identifier%select{|, index}0 or 'self' in lifetime dependence specifier",
+      (bool))
 
 ERROR(expected_rparen_after_lifetime_dependence, PointsToFirstBadToken,
       "expected ')' after parameter list in lifetime dependence specifier", ())
diff --git a/include/swift/Parse/Parser.h b/include/swift/Parse/Parser.h
index c06cdc402a9e8..9cacd167cfd9e 100644
--- a/include/swift/Parse/Parser.h
+++ b/include/swift/Parse/Parser.h
@@ -1158,7 +1158,8 @@ class Parser {
 
   /// Common utility to parse swift @lifetime decl attribute and SIL @lifetime
   /// type modifier.
-  ParserResult<LifetimeEntry> parseLifetimeEntry(SourceLoc loc);
+  ParserResult<LifetimeEntry> parseLifetimeEntry(SourceLoc loc,
+                                                 bool allowIndices);
 
   /// Parse a specific attribute.
   ParserStatus parseDeclAttribute(DeclAttributes &Attributes, SourceLoc AtLoc,
diff --git a/lib/Parse/ParseDecl.cpp b/lib/Parse/ParseDecl.cpp
index e5f629231bf9b..e6a1991809778 100644
--- a/lib/Parse/ParseDecl.cpp
+++ b/lib/Parse/ParseDecl.cpp
@@ -2545,7 +2545,7 @@ static std::optional<Identifier> parseSingleAttrOptionImpl(
 }
 
 static std::optional<LifetimeDescriptor>
-parseLifetimeDescriptor(Parser &P,
+parseLifetimeDescriptor(Parser &P, bool allowIndices,
                         ParsedLifetimeDependenceKind lifetimeDependenceKind =
                             ParsedLifetimeDependenceKind::Default) {
   auto token = P.Tok;
@@ -2577,6 +2577,13 @@ parseLifetimeDescriptor(Parser &P,
   case tok::integer_literal: {
     SourceLoc loc;
     unsigned index;
+    if (!allowIndices) {
+      P.diagnose(
+          token,
+          diag::expected_identifier_or_index_or_self_after_lifetime_dependence,
+          /* allow indices */ false);
+      return std::nullopt;
+    }
     if (P.parseUnsignedInteger(
             index, loc, diag::expected_param_index_lifetime_dependence)) {
       return std::nullopt;
@@ -2590,7 +2597,8 @@ parseLifetimeDescriptor(Parser &P,
   default: {
     P.diagnose(
         token,
-        diag::expected_identifier_or_index_or_self_after_lifetime_dependence);
+        diag::expected_identifier_or_index_or_self_after_lifetime_dependence,
+        allowIndices);
     return std::nullopt;
   }
   }
@@ -2601,7 +2609,7 @@ ParserResult<LifetimeAttr> Parser::parseLifetimeAttribute(StringRef attrName,
                                                           SourceLoc loc) {
   ParserStatus status;
 
-  auto lifetimeEntry = parseLifetimeEntry(loc);
+  auto lifetimeEntry = parseLifetimeEntry(loc, /*allowIndices=*/false);
   if (lifetimeEntry.isNull()) {
     status.setIsParseError();
     return status;
@@ -5077,7 +5085,7 @@ ParserStatus Parser::parseTypeAttribute(TypeOrCustomAttr &result,
   }
 
   case TypeAttrKind::Lifetime: {
-    const auto entryResult = parseLifetimeEntry(AtLoc);
+    const auto entryResult = parseLifetimeEntry(AtLoc, /*allowIndices=*/false);
     if (entryResult.isNull()) {
       return makeParserError();
     }
@@ -5164,7 +5172,8 @@ ParserStatus Parser::parseTypeAttribute(TypeOrCustomAttr &result,
   llvm_unreachable("bad attribute kind");
 }
 
-ParserResult<LifetimeEntry> Parser::parseLifetimeEntry(SourceLoc loc) {
+ParserResult<LifetimeEntry> Parser::parseLifetimeEntry(SourceLoc loc,
+                                                       bool allowIndices) {
   ParserStatus status;
 
   auto getLifetimeDependenceKind =
@@ -5198,7 +5207,7 @@ ParserResult<LifetimeEntry> Parser::parseLifetimeEntry(SourceLoc loc) {
   std::optional<LifetimeDescriptor> targetDescriptor;
   if (Tok.isAny(tok::identifier, tok::integer_literal, tok::kw_self) &&
       peekToken().is(tok::colon)) {
-    targetDescriptor = parseLifetimeDescriptor(*this);
+    targetDescriptor = parseLifetimeDescriptor(*this, allowIndices);
     if (!targetDescriptor) {
       status.setIsParseError();
       return status;
@@ -5223,8 +5232,8 @@ ParserResult<LifetimeEntry> Parser::parseLifetimeEntry(SourceLoc loc) {
           consumeToken();
         }
 
-        auto sourceDescriptor =
-            parseLifetimeDescriptor(*this, lifetimeDependenceKind);
+        auto sourceDescriptor = parseLifetimeDescriptor(*this, allowIndices,
+                                                        lifetimeDependenceKind);
         if (!sourceDescriptor) {
           invalidSourceDescriptor = true;
           listStatus.setIsParseError();
@@ -5241,7 +5250,8 @@ ParserResult<LifetimeEntry> Parser::parseLifetimeEntry(SourceLoc loc) {
   if (!foundParamId) {
     diagnose(
         Tok,
-        diag::expected_identifier_or_index_or_self_after_lifetime_dependence);
+        diag::expected_identifier_or_index_or_self_after_lifetime_dependence,
+        /* allow indices */ isInSILMode());
     status.setIsParseError();
     return status;
   }
@@ -5583,7 +5593,7 @@ ParserStatus Parser::ParsedTypeAttributeList::slowParse(Parser &P) {
       }
       P.consumeToken(); // consume '@'
       auto loc = P.consumeToken(); // consume 'lifetime'
-      auto result = P.parseLifetimeEntry(loc);
+      auto result = P.parseLifetimeEntry(loc, /*allowIndices=*/true);
       if (result.isNull()) {
         status |= result;
         continue;
diff --git a/test/Parse/lifetime_attr.swift b/test/Parse/lifetime_attr.swift
index 218dc8b5bbe70..53349171731a7 100644
--- a/test/Parse/lifetime_attr.swift
+++ b/test/Parse/lifetime_attr.swift
@@ -24,7 +24,7 @@ func testMissingLParenError(_ ne: NE) -> NE {
   ne
 }
 
-@_lifetime() // expected-error{{expected 'copy', 'borrow', or '&' followed by an identifier, index or 'self' in lifetime dependence specifier}}
+@_lifetime() // expected-error{{expected 'copy', 'borrow', or '&' followed by an identifier or 'self' in lifetime dependence specifier}}
 func testMissingDependence(_ ne: NE) -> NE {
   ne
 }
diff --git a/test/Sema/lifetime_attr.swift b/test/Sema/lifetime_attr.swift
index 9c1cb4016c664..dc90e4f5ffddd 100644
--- a/test/Sema/lifetime_attr.swift
+++ b/test/Sema/lifetime_attr.swift
@@ -17,7 +17,12 @@ func invalidAttrOnNonExistingSelf(_ ne: NE) -> NE {
   ne
 }
 
-@_lifetime(2) // expected-error{{invalid parameter index specified '2'}}
+@_lifetime(copy 0) // expected-error{{expected 'copy', 'borrow', or '&' followed by an identifier or 'self' in lifetime dependence specifier}}
+func invalidAttrOnExistingParamIndex(_ ne: NE) -> NE {
+  ne
+}
+
+@_lifetime(2) // expected-error{{expected 'copy', 'borrow', or '&' followed by an identifier or 'self' in lifetime dependence specifier}}
 func invalidAttrOnNonExistingParamIndex(_ ne: NE) -> NE {
   ne
 }
diff --git a/test/Sema/lifetime_depend_infer.swift b/test/Sema/lifetime_depend_infer.swift
index e87b6e43fc95b..71c7998920639 100644
--- a/test/Sema/lifetime_depend_infer.swift
+++ b/test/Sema/lifetime_depend_infer.swift
@@ -849,7 +849,7 @@ struct NoncopyableSelfAccessors: ~Copyable & ~Escapable {
 
 // Invalid keyword for the dependence kind.
 //
-@_lifetime(a: inout a) // expected-error{{expected 'copy', 'borrow', or '&' followed by an identifier, index or 'self' in lifetime dependence specifier}}
+@_lifetime(a: inout a) // expected-error{{expected 'copy', 'borrow', or '&' followed by an identifier or 'self' in lifetime dependence specifier}}
 func f_inout_bad_keyword(a: inout MutableRawSpan) {}
 
 // Don't allow a useless borrow dependency on an inout param--it is misleading.
diff --git a/test/Sema/lifetime_dependence_functype.swift b/test/Sema/lifetime_dependence_functype.swift
index 871af3d61b9c7..d7ce9a85d514e 100644
--- a/test/Sema/lifetime_dependence_functype.swift
+++ b/test/Sema/lifetime_dependence_functype.swift
@@ -19,7 +19,7 @@ func transfer(_ ne: NE) -> NE {
 }
 
 @_lifetime(copy ne)
-func applyAnnotatedTransfer(ne: NE, @_lifetime(0) transfer: (NE) -> NE) -> NE { // expected-error{{'@_lifetime' attribute cannot be applied to this declaration}}
+func applyAnnotatedTransfer(ne: NE, @_lifetime(copy ne) transfer: (_ ne: NE) -> NE) -> NE { // expected-error{{'@_lifetime' attribute cannot be applied to this declaration}}
   transfer(ne)
 }
 
@@ -61,7 +61,9 @@ typealias InvalidAttrOnNonExistingParamType = @_lifetime(copy nonexisting) (_ ne
 
 typealias InvalidAttrOnNonExistingSelfType = @_lifetime(copy self) (_ ne: NE) -> NE // expected-error{{invalid lifetime dependence specifier on non-existent self}}
 
-typealias InvalidAttrOnNonExistingParamIndexType = @_lifetime(2) (_ ne: NE) -> NE // expected-error{{invalid parameter index specified '2'}}
+typealias InvalidAttrOnExistingParamIndexType = @_lifetime(0) (_ ne: NE) -> NE // expected-error{{expected 'copy', 'borrow', or '&' followed by an identifier or 'self' in lifetime dependence specifier}}
+
+typealias InvalidAttrOnNonExistingParamIndexType = @_lifetime(2) (_ ne: NE) -> NE // expected-error{{expected 'copy', 'borrow', or '&' followed by an identifier or 'self' in lifetime dependence specifier}}
 
 typealias InvalidDuplicateLifetimeDependenceType = @_lifetime(copy ne, borrow ne) (_ ne: borrowing NE) -> NE // expected-error{{duplicate lifetime dependence specifier}}