diff --git a/mlir/include/mlir/IR/DialectImplementation.h b/mlir/include/mlir/IR/DialectImplementation.h
--- a/mlir/include/mlir/IR/DialectImplementation.h
+++ b/mlir/include/mlir/IR/DialectImplementation.h
@@ -139,7 +139,8 @@
   virtual ParseResult parseFloat(double &result) = 0;
 
   /// Parse an integer value from the stream.
-  template <typename IntT> ParseResult parseInteger(IntT &result) {
+  template <typename IntT>
+  ParseResult parseInteger(IntT &result) {
     auto loc = getCurrentLocation();
     OptionalParseResult parseResult = parseOptionalInteger(result);
     if (!parseResult.hasValue())
@@ -148,21 +149,23 @@
   }
 
   /// Parse an optional integer value from the stream.
-  virtual OptionalParseResult parseOptionalInteger(uint64_t &result) = 0;
+  virtual OptionalParseResult parseOptionalInteger(APInt &result) = 0;
 
   template <typename IntT>
   OptionalParseResult parseOptionalInteger(IntT &result) {
     auto loc = getCurrentLocation();
 
     // Parse the unsigned variant.
-    uint64_t uintResult;
+    APInt uintResult;
     OptionalParseResult parseResult = parseOptionalInteger(uintResult);
     if (!parseResult.hasValue() || failed(*parseResult))
       return parseResult;
 
-    // Try to convert to the provided integer type.
-    result = IntT(uintResult);
-    if (uint64_t(result) != uintResult)
+    // Try to convert to the provided integer type.  sextOrTrunc is correct even
+    // for unsigned types because parseOptionalInteger ensures the sign bit is
+    // zero for non-negated integers.
+    result = (IntT)uintResult.sextOrTrunc(sizeof(IntT) * 8).getLimitedValue();
+    if (APInt(uintResult.getBitWidth(), result) != uintResult)
       return emitError(loc, "integer value too large");
     return success();
   }
@@ -172,13 +175,14 @@
   /// unlike `OpBuilder::getType`, this method does not implicitly insert a
   /// context parameter.
   template <typename T, typename... ParamsT>
-  T getChecked(llvm::SMLoc loc, ParamsT &&...params) {
+  T getChecked(llvm::SMLoc loc, ParamsT &&... params) {
     return T::getChecked([&] { return emitError(loc); },
                          std::forward<ParamsT>(params)...);
   }
   /// A variant of `getChecked` that uses the result of `getNameLoc` to emit
   /// errors.
-  template <typename T, typename... ParamsT> T getChecked(ParamsT &&...params) {
+  template <typename T, typename... ParamsT>
+  T getChecked(ParamsT &&... params) {
     return T::getChecked([&] { return emitError(getNameLoc()); },
                          std::forward<ParamsT>(params)...);
   }
@@ -331,7 +335,8 @@
   virtual ParseResult parseType(Type &result) = 0;
 
   /// Parse a type of a specific kind, e.g. a FunctionType.
-  template <typename TypeType> ParseResult parseType(TypeType &result) {
+  template <typename TypeType>
+  ParseResult parseType(TypeType &result) {
     llvm::SMLoc loc = getCurrentLocation();
 
     // Parse any kind of type.
diff --git a/mlir/include/mlir/IR/OpImplementation.h b/mlir/include/mlir/IR/OpImplementation.h
--- a/mlir/include/mlir/IR/OpImplementation.h
+++ b/mlir/include/mlir/IR/OpImplementation.h
@@ -435,21 +435,23 @@
   }
 
   /// Parse an optional integer value from the stream.
-  virtual OptionalParseResult parseOptionalInteger(uint64_t &result) = 0;
+  virtual OptionalParseResult parseOptionalInteger(APInt &result) = 0;
 
   template <typename IntT>
   OptionalParseResult parseOptionalInteger(IntT &result) {
     auto loc = getCurrentLocation();
 
     // Parse the unsigned variant.
-    uint64_t uintResult;
+    APInt uintResult;
     OptionalParseResult parseResult = parseOptionalInteger(uintResult);
     if (!parseResult.hasValue() || failed(*parseResult))
       return parseResult;
 
-    // Try to convert to the provided integer type.
-    result = IntT(uintResult);
-    if (uint64_t(result) != uintResult)
+    // Try to convert to the provided integer type.  sextOrTrunc is correct even
+    // for unsigned types because parseOptionalInteger ensures the sign bit is
+    // zero for non-negated integers.
+    result = (IntT)uintResult.sextOrTrunc(sizeof(IntT) * 8).getLimitedValue();
+    if (APInt(uintResult.getBitWidth(), result) != uintResult)
       return emitError(loc, "integer value too large");
     return success();
   }
diff --git a/mlir/lib/Parser/DialectSymbolParser.cpp b/mlir/lib/Parser/DialectSymbolParser.cpp
--- a/mlir/lib/Parser/DialectSymbolParser.cpp
+++ b/mlir/lib/Parser/DialectSymbolParser.cpp
@@ -94,7 +94,7 @@
   }
 
   /// Parse an optional integer value from the stream.
-  OptionalParseResult parseOptionalInteger(uint64_t &result) override {
+  OptionalParseResult parseOptionalInteger(APInt &result) override {
     return parser.parseOptionalInteger(result);
   }
 
diff --git a/mlir/lib/Parser/Parser.h b/mlir/lib/Parser/Parser.h
--- a/mlir/lib/Parser/Parser.h
+++ b/mlir/lib/Parser/Parser.h
@@ -128,7 +128,7 @@
   ParseResult parseToken(Token::Kind expectedToken, const Twine &message);
 
   /// Parse an optional integer value from the stream.
-  OptionalParseResult parseOptionalInteger(uint64_t &result);
+  OptionalParseResult parseOptionalInteger(APInt &result);
 
   /// Parse a floating point value from an integer literal token.
   ParseResult parseFloatFromIntegerLiteral(Optional<APFloat> &result,
diff --git a/mlir/lib/Parser/Parser.cpp b/mlir/lib/Parser/Parser.cpp
--- a/mlir/lib/Parser/Parser.cpp
+++ b/mlir/lib/Parser/Parser.cpp
@@ -96,7 +96,7 @@
 }
 
 /// Parse an optional integer value from the stream.
-OptionalParseResult Parser::parseOptionalInteger(uint64_t &result) {
+OptionalParseResult Parser::parseOptionalInteger(APInt &result) {
   Token curToken = getToken();
   if (curToken.isNot(Token::integer, Token::minus))
     return llvm::None;
@@ -106,10 +106,19 @@
   if (parseToken(Token::integer, "expected integer value"))
     return failure();
 
-  auto val = curTok.getUInt64IntegerValue();
-  if (!val)
+  StringRef spelling = curTok.getSpelling();
+  bool isHex = spelling.size() > 1 && spelling[1] == 'x';
+  if (spelling.getAsInteger(isHex ? 0 : 10, result))
     return emitError(curTok.getLoc(), "integer value too large");
-  result = negative ? -*val : *val;
+
+  // Make sure we have a zero at the top so we return the right signedness.
+  if (result.isNegative())
+    result = result.zext(result.getBitWidth() + 1);
+
+  // Process the negative sign if present.
+  if (negative)
+    result.negate();
+
   return success();
 }
 
@@ -1217,7 +1226,7 @@
   }
 
   /// Parse an optional integer value from the stream.
-  OptionalParseResult parseOptionalInteger(uint64_t &result) override {
+  OptionalParseResult parseOptionalInteger(APInt &result) override {
     return parser.parseOptionalInteger(result);
   }