diff --git a/include/swift/AST/DiagnosticsParse.def b/include/swift/AST/DiagnosticsParse.def
index cf2d07d817aed..55819a27def21 100644
--- a/include/swift/AST/DiagnosticsParse.def
+++ b/include/swift/AST/DiagnosticsParse.def
@@ -1295,7 +1295,11 @@ ERROR(swift_native_objc_runtime_base_must_be_identifier,none,
       "@_swift_native_objc_runtime_base class name must be an identifier", ())
 
 ERROR(attr_interpolated_string,none,
-"%0 cannot be an interpolated string literal", (StringRef))
+"'%0' cannot be an interpolated string literal", (StringRef))
+ERROR(attr_multiline_string,none,
+"'%0' cannot be a multiline string literal", (StringRef))
+ERROR(attr_extended_escaping_string,none,
+"'%0' cannot be an extended escaping string literal", (StringRef))
 
 ERROR(attr_only_at_non_local_scope, none,
       "attribute '%0' can only be used in a non-local scope", (StringRef))
diff --git a/lib/Parse/Lexer.cpp b/lib/Parse/Lexer.cpp
index d77fda48834d9..cbdf56e0dcdef 100644
--- a/lib/Parse/Lexer.cpp
+++ b/lib/Parse/Lexer.cpp
@@ -2108,26 +2108,6 @@ StringRef Lexer::getEncodedStringSegment(StringRef Bytes,
   // range check subscripting on the StringRef.
   const char *BytesPtr = Bytes.begin();
 
-  // Special case when being called from EncodedDiagnosticMessage(...).
-  // This allows multiline and delimited strings to work in attributes.
-  // The string has already been validated by the initial parse.
-  if (IndentToStrip == ~0u && CustomDelimiterLen == ~0u) {
-    IndentToStrip = CustomDelimiterLen = 0;
-
-    // Restore trailing indent removal for multiline.
-    const char *Backtrack = BytesPtr - 1;
-    if (Backtrack[-1] == '"' && Backtrack[-2] == '"') {
-      Backtrack -= 2;
-      for (const char *Trailing = Bytes.end() - 1;
-           *Trailing == ' ' || *Trailing == '\t'; Trailing--)
-        IndentToStrip++;
-    }
-
-    // Restore delimiter if any.
-    while (*--Backtrack == '#')
-      CustomDelimiterLen++;
-  }
-
   bool IsEscapedNewline = false;
   while (BytesPtr < Bytes.end()) {
     char CurChar = *BytesPtr++;
diff --git a/lib/Parse/ParseDecl.cpp b/lib/Parse/ParseDecl.cpp
index 6a05539a7ebf9..c00fba15a8650 100644
--- a/lib/Parse/ParseDecl.cpp
+++ b/lib/Parse/ParseDecl.cpp
@@ -300,6 +300,16 @@ bool Parser::parseTopLevel() {
 static Optional<StringRef>
 getStringLiteralIfNotInterpolated(Parser &P, SourceLoc Loc, const Token &Tok,
                                   StringRef DiagText) {
+  // FIXME: Support extended escaping / multiline string literal.
+  if (Tok.getCustomDelimiterLen()) {
+    P.diagnose(Loc, diag::attr_extended_escaping_string, DiagText);
+    return None;
+  }
+  if (Tok.isMultilineString()) {
+    P.diagnose(Loc, diag::attr_multiline_string, DiagText);
+    return None;
+  }
+
   SmallVector<Lexer::StringSegment, 1> Segments;
   P.L->getStringLiteralSegments(Tok, Segments);
   if (Segments.size() != 1 ||
diff --git a/lib/Sema/TypeChecker.h b/lib/Sema/TypeChecker.h
index 7d64ecad386f9..5e55ef3344b55 100644
--- a/lib/Sema/TypeChecker.h
+++ b/lib/Sema/TypeChecker.h
@@ -2164,7 +2164,7 @@ class EncodedDiagnosticMessage {
 public:
   /// \param S A string with an encoded message
   EncodedDiagnosticMessage(StringRef S)
-      : Message(Lexer::getEncodedStringSegment(S, Buf, true, true, ~0, ~0)) {}
+      : Message(Lexer::getEncodedStringSegment(S, Buf)) {}
 
   /// The unescaped message to display to the user.
   const StringRef Message;
diff --git a/test/Parse/diagnose_availability.swift b/test/Parse/diagnose_availability.swift
index 1b35b9af90fa5..ad41d26644a7e 100644
--- a/test/Parse/diagnose_availability.swift
+++ b/test/Parse/diagnose_availability.swift
@@ -62,3 +62,22 @@ func swiftDeprecatedObsoleted() {}
 // expected-warning@-1 {{expected 'introduced', 'deprecated', or 'obsoleted' in 'available' attribute for platform 'swift'}}
 func swiftMessage() {}
 
+@available(*, unavailable, message: "\("message")")
+// expected-error@-1{{'message' cannot be an interpolated string literal}}
+func interpolatedMessage() {}
+
+// expected-error@+1{{'message' cannot be a multiline string literal}}
+@available(*, unavailable, message: """
+  foobar message.
+  """)
+func multilineMessage() {}
+
+// expected-error@+1{{'message' cannot be an extended escaping string literal}}
+@available(*, unavailable, message: #"""
+  foobar message.
+  """#)
+func extendedEscapedMultilineMessage() {}
+
+// expected-error@+1{{'renamed' cannot be an extended escaping string literal}}
+@available(*, unavailable, renamed: #"avialable()"#)
+func extenedEscpaedRenamed() {}