diff --git a/mlir/lib/Parser/AffineParser.cpp b/mlir/lib/Parser/AffineParser.cpp
--- a/mlir/lib/Parser/AffineParser.cpp
+++ b/mlir/lib/Parser/AffineParser.cpp
@@ -269,13 +269,13 @@
 ///
 ///   affine-expr ::= bare-id
 AffineExpr AffineParser::parseBareIdExpr() {
-  if (getToken().isNot(Token::bare_identifier))
+  if (!getToken().isBareIdentifier())
     return emitWrongTokenError("expected bare identifier"), nullptr;
 
   StringRef sRef = getTokenSpelling();
   for (auto entry : dimsAndSymbols) {
     if (entry.first == sRef) {
-      consumeToken(Token::bare_identifier);
+      consumeToken();
       return entry.second;
     }
   }
@@ -458,7 +458,7 @@
 /// expressions of the affine map. Update our state to store the
 /// dimensional/symbolic identifier.
 ParseResult AffineParser::parseIdentifierDefinition(AffineExpr idExpr) {
-  if (getToken().isNot(Token::bare_identifier))
+  if (!getToken().isBareIdentifier())
     return emitWrongTokenError("expected bare identifier");
 
   auto name = getTokenSpelling();
@@ -466,7 +466,7 @@
     if (entry.first == name)
       return emitError("redefinition of identifier '" + name + "'");
   }
-  consumeToken(Token::bare_identifier);
+  consumeToken();
 
   dimsAndSymbols.push_back({name, idExpr});
   return success();
diff --git a/mlir/lib/Parser/Token.h b/mlir/lib/Parser/Token.h
--- a/mlir/lib/Parser/Token.h
+++ b/mlir/lib/Parser/Token.h
@@ -58,6 +58,9 @@
   /// Return true if this is one of the keyword token kinds (e.g. kw_if).
   bool isKeyword() const;
 
+  /// Returns true if this token can be represented as a bare identifier.
+  bool isBareIdentifier() const;
+
   // Helpers to decode specific sorts of tokens.
 
   /// For an integer token, return its value as an unsigned.  If it doesn't fit,
diff --git a/mlir/lib/Parser/Token.cpp b/mlir/lib/Parser/Token.cpp
--- a/mlir/lib/Parser/Token.cpp
+++ b/mlir/lib/Parser/Token.cpp
@@ -187,3 +187,18 @@
 #include "TokenKinds.def"
   }
 }
+
+/// Returns true if the given string can be represented as a bare identifier.
+bool Token::isBareIdentifier() const {
+  StringRef spelling = getSpelling();
+  if (spelling.empty() || (!isalpha(spelling[0]) && spelling[0] != '_'))
+    return false;
+
+  // By making this unsigned, the value passed in to isalnum will always be
+  // in the range 0-255. This is important when building with MSVC because
+  // its implementation will assert. This situation can arise when dealing
+  // with UTF-8 multibyte characters.
+  return llvm::all_of(spelling.drop_front(), [](unsigned char c) {
+    return isalnum(c) || c == '_' || c == '$' || c == '.';
+  });
+}