diff --git a/include/swift/Parse/Parser.h b/include/swift/Parse/Parser.h
index 055f86cd85ee6..40f6d91ab1403 100644
--- a/include/swift/Parse/Parser.h
+++ b/include/swift/Parse/Parser.h
@@ -1259,6 +1259,9 @@ class Parser {
 
     /// Whether the type is for a closure attribute.
     CustomAttribute,
+
+    /// Whether the type is a destination of a cast.
+    CastDestination,
   };
 
   ParserResult<TypeRepr> parseType();
@@ -1297,8 +1300,9 @@ class Parser {
   ///   positioned at '.f'.
   /// - If there is no base type qualifier (e.g. when parsing just 'f'), returns
   ///   an empty parser error.
-  ParserResult<TypeRepr> parseTypeIdentifier(
-      bool isParsingQualifiedDeclBaseType = false);
+  ParserResult<TypeRepr>
+  parseTypeIdentifier(bool isParsingQualifiedDeclBaseType = false,
+                      ParseTypeReason reason = ParseTypeReason::Unspecified);
   ParserResult<TypeRepr> parseOldStyleProtocolComposition();
   ParserResult<TypeRepr> parseAnyType();
   ParserResult<TypeRepr> parseSILBoxType(GenericParamList *generics,
diff --git a/lib/Parse/ParseExpr.cpp b/lib/Parse/ParseExpr.cpp
index 5de9eb323bb54..570d703970052 100644
--- a/lib/Parse/ParseExpr.cpp
+++ b/lib/Parse/ParseExpr.cpp
@@ -74,7 +74,8 @@ ParserResult<Expr> Parser::parseExprImpl(Diag<> Message,
 ParserResult<Expr> Parser::parseExprIs() {
   SourceLoc isLoc = consumeToken(tok::kw_is);
 
-  ParserResult<TypeRepr> type = parseType(diag::expected_type_after_is);
+  ParserResult<TypeRepr> type =
+      parseType(diag::expected_type_after_is, ParseTypeReason::CastDestination);
   if (type.hasCodeCompletion())
     return makeParserCodeCompletionResult<Expr>();
   if (type.isNull())
@@ -101,7 +102,8 @@ ParserResult<Expr> Parser::parseExprAs() {
     exclaimLoc = consumeToken(tok::exclaim_postfix);
   }
 
-  ParserResult<TypeRepr> type = parseType(diag::expected_type_after_as);
+  ParserResult<TypeRepr> type =
+      parseType(diag::expected_type_after_as, ParseTypeReason::CastDestination);
 
   if (type.hasCodeCompletion())
     return makeParserCodeCompletionResult<Expr>();
diff --git a/lib/Parse/ParseType.cpp b/lib/Parse/ParseType.cpp
index 6d1692ce68178..096f22369e7f6 100644
--- a/lib/Parse/ParseType.cpp
+++ b/lib/Parse/ParseType.cpp
@@ -14,16 +14,16 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "swift/Parse/Parser.h"
 #include "swift/AST/ASTWalker.h"
 #include "swift/AST/Attr.h"
 #include "swift/AST/GenericParamList.h"
 #include "swift/AST/TypeRepr.h"
-#include "swift/Parse/Lexer.h"
 #include "swift/Parse/CodeCompletionCallbacks.h"
-#include "swift/Parse/SyntaxParsingContext.h"
+#include "swift/Parse/Lexer.h"
 #include "swift/Parse/ParsedSyntaxBuilders.h"
 #include "swift/Parse/ParsedSyntaxRecorder.h"
+#include "swift/Parse/Parser.h"
+#include "swift/Parse/SyntaxParsingContext.h"
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/Twine.h"
@@ -180,7 +180,7 @@ ParserResult<TypeRepr> Parser::parseTypeSimple(
   case tok::kw_Self:
   case tok::kw_Any:
   case tok::identifier: {
-    ty = parseTypeIdentifier();
+    ty = parseTypeIdentifier(/*isParsingQualifiedDeclBaseType=*/false, reason);
     break;
   }
   case tok::l_paren:
@@ -679,7 +679,8 @@ ParserStatus Parser::parseGenericArguments(SmallVectorImpl<TypeRepr *> &Args,
 ///     identifier generic-args? ('.' identifier generic-args?)*
 ///
 ParserResult<TypeRepr>
-Parser::parseTypeIdentifier(bool isParsingQualifiedDeclBaseType) {
+Parser::parseTypeIdentifier(bool isParsingQualifiedDeclBaseType,
+                            ParseTypeReason reason) {
   // If parsing a qualified declaration name, return error if base type cannot
   // be parsed.
   if (isParsingQualifiedDeclBaseType && !canParseBaseTypeForQualifiedDeclName())
@@ -722,9 +723,16 @@ Parser::parseTypeIdentifier(bool isParsingQualifiedDeclBaseType) {
       SourceLoc LAngle, RAngle;
       SmallVector<TypeRepr*, 8> GenericArgs;
       if (startsWithLess(Tok)) {
-        auto genericArgsStatus = parseGenericArguments(GenericArgs, LAngle, RAngle);
-        if (genericArgsStatus.isErrorOrHasCompletion())
-          return genericArgsStatus;
+        // Only attempt to parse a generic argument list in a cast destination
+        // type if the token text is just "<", because it can be an operator,
+        // for example: "1 as Int16 << 7".
+        if (Tok.getText().equals("<") ||
+            reason != ParseTypeReason::CastDestination) {
+          auto genericArgsStatus =
+              parseGenericArguments(GenericArgs, LAngle, RAngle);
+          if (genericArgsStatus.isErrorOrHasCompletion())
+            return genericArgsStatus;
+        }
       }
       EndLoc = Loc.getEndLoc();
 
diff --git a/test/Parse/generic_disambiguation.swift b/test/Parse/generic_disambiguation.swift
index ebb900e3e8c47..8124c02b1aa6d 100644
--- a/test/Parse/generic_disambiguation.swift
+++ b/test/Parse/generic_disambiguation.swift
@@ -76,3 +76,22 @@ A<B?>(x: 0) // parses as type // expected-warning{{unused}}
 _ = a < b ? c : d
 
 A<(B) throws -> D>(x: 0) // expected-warning{{unused}}
+
+// https://github.com/apple/swift/issues/43053
+do {
+  1 as! A<B>.F << 2 // expected-warning {{cast from 'Int' to unrelated type 'A<B>.F' always fails}}
+  // expected-error@-1 {{referencing operator function '<<' on 'BinaryInteger' requires that 'A<B>.F' conform to 'BinaryInteger'}}
+  1 as! A<B> << 2 // expected-warning {{cast from 'Int' to unrelated type 'A<B>' always fails}}
+  // expected-error@-1 {{referencing operator function '<<' on 'BinaryInteger' requires that 'A<B>' conform to 'BinaryInteger'}}
+  let _ = 1 as Int16 << 7
+  let _ = 1 as? Int16 << 7 // expected-error {{value of optional type 'Int16?' must be unwrapped to a value of type 'Int16'}}
+  // expected-warning@-1 {{conditional downcast from literal to 'Int16' always fails; consider using 'as' coercion}}
+  // expected-note@-2 {{coalesce using '??' to provide a default when the optional value contains 'nil'}}
+  // expected-note@-3 {{force-unwrap using '!' to abort execution if the optional value contains 'nil'}}
+  let _ = 1 is Int16 << 7 // expected-warning {{conditional downcast from literal to 'Int16' always fails; consider using 'as' coercion}}
+  // expected-error@-1 {{binary operator '<<' cannot be applied to operands of type 'Bool' and 'Int'}}
+  let _ = 1 as! Int16 << 7 // expected-warning {{conditional downcast from literal to 'Int16' always fails; consider using 'as' coercion}}
+  let _ = 1 as Int16 <= 7
+  // FIXME: this should not produce any errors.
+  let _ = 1 as Int16 < 7 // expected-error {{expected type}}
+}