Index: llvm/include/llvm/MC/MCParser/MCAsmLexer.h
===================================================================
--- llvm/include/llvm/MC/MCParser/MCAsmLexer.h
+++ llvm/include/llvm/MC/MCParser/MCAsmLexer.h
@@ -55,6 +55,7 @@
   bool LexMasmStrings = false;
   bool UseMasmDefaultRadix = false;
   unsigned DefaultRadix = 10;
+  bool LexHLASMIntegers = false;
   AsmCommentConsumer *CommentConsumer = nullptr;
 
   MCAsmLexer();
@@ -171,6 +172,9 @@
   /// Set whether to lex masm-style string literals, such as 'Can''t find file'
   /// and "This ""value"" not found".
   void setLexMasmStrings(bool V) { LexMasmStrings = V; }
+
+  /// Set whether to lex HLASM-flavour integers. For now this is only [0-9]*
+  void setLexHLASMIntegers(bool V) { LexHLASMIntegers = V; }
 };
 
 } // end namespace llvm
Index: llvm/lib/MC/MCParser/AsmLexer.cpp
===================================================================
--- llvm/lib/MC/MCParser/AsmLexer.cpp
+++ llvm/lib/MC/MCParser/AsmLexer.cpp
@@ -320,6 +320,24 @@
 ///   Hex integer: 0x[0-9a-fA-F]+ or [0x]?[0-9][0-9a-fA-F]*[hH]
 ///   Decimal integer: [1-9][0-9]*
 AsmToken AsmLexer::LexDigit() {
+  // HLASM-flavour decimal integer: [0-9]*
+  // FIXME: Later on, support for fb has to be added in
+  // as they probably would be needed for asm goto
+  if (LexHLASMIntegers) {
+    // You can have leading 0s in HLASM-flavour integers
+    // They don't mean octal integers
+    unsigned Radix = doHexLookAhead(CurPtr, 10, /*LexMasmIntegers=*/false);
+    StringRef Result(TokStart, CurPtr - TokStart);
+
+    APInt Value(128, 0, true);
+    // The getAsInteger routine will remove leading zeros when
+    // when computing Value.
+    if (Result.getAsInteger(Radix, Value))
+      return ReturnError(TokStart, "invalid " + radixName(Radix) + " number");
+
+    return intToken(Result, Value);
+  }
+
   // MASM-flavor binary integer: [01]+[yY] (if DefaultRadix < 16, [bByY])
   // MASM-flavor octal integer: [0-7]+[oOqQ]
   // MASM-flavor decimal integer: [0-9]+[tT] (if DefaultRadix < 16, [dDtT])
Index: llvm/unittests/MC/SystemZ/SystemZAsmLexerTest.cpp
===================================================================
--- llvm/unittests/MC/SystemZ/SystemZAsmLexerTest.cpp
+++ llvm/unittests/MC/SystemZ/SystemZAsmLexerTest.cpp
@@ -109,6 +109,21 @@
       Lexer.Lex();
     }
   }
+
+  void lexAndCheckIntegerTokensAndValues(StringRef AsmStr,
+                                         SmallVector<int64_t> ExpectedValues) {
+    // Get reference to AsmLexer.
+    MCAsmLexer &Lexer = Parser->getLexer();
+    // Loop through all expected tokens and expected values.
+    for (size_t I = 0; I < ExpectedValues.size(); ++I) {
+      // Skip any EndOfStatement tokens, we're not concerned with them.
+      if (Lexer.getTok().getKind() == AsmToken::EndOfStatement)
+        continue;
+      EXPECT_EQ(Lexer.getTok().getKind(), AsmToken::Integer);
+      EXPECT_EQ(Lexer.getTok().getIntVal(), ExpectedValues[I]);
+      Lexer.Lex();
+    }
+  }
 };
 
 TEST_F(SystemZAsmLexerTest, CheckDontRestrictCommentStringToStartOfStatement) {
@@ -367,4 +382,42 @@
 
   lexAndCheckTokens(AsmStr, ExpectedTokens);
 }
+
+TEST_F(SystemZAsmLexerTest, CheckValidHLASMIntegers) {
+  StringRef AsmStr = "123\n000123\n1999\n007\n12300\n12021";
+  // StringRef AsmStr = "123";
+  // Setup.
+  setupCallToAsmParser(AsmStr);
+  Parser->getLexer().setLexHLASMIntegers(true);
+
+  // Lex initially to get the string.
+  Parser->getLexer().Lex();
+
+  // SmallVector<int64_t> ExpectedValues({123});
+  SmallVector<int64_t> ExpectedValues({123, 123, 1999, 7, 12300, 12021});
+  lexAndCheckIntegerTokensAndValues(AsmStr, ExpectedValues);
+}
+
+TEST_F(SystemZAsmLexerTest, CheckInvalidHLASMIntegers) {
+  StringRef AsmStr = "0b0101\n0xDEADBEEF\nfffh";
+
+  // Setup.
+  setupCallToAsmParser(AsmStr);
+  Parser->getLexer().setLexHLASMIntegers(true);
+
+  // Lex initially to get the string.
+  Parser->getLexer().Lex();
+
+  SmallVector<AsmToken::TokenKind> ExpectedTokens;
+  ExpectedTokens.push_back(AsmToken::Integer);        // "0"
+  ExpectedTokens.push_back(AsmToken::Identifier);     // "b0101"
+  ExpectedTokens.push_back(AsmToken::EndOfStatement); // "\n"
+  ExpectedTokens.push_back(AsmToken::Integer);        // "0"
+  ExpectedTokens.push_back(AsmToken::Identifier);     // "xDEADBEEF"
+  ExpectedTokens.push_back(AsmToken::EndOfStatement); // "\n"
+  ExpectedTokens.push_back(AsmToken::Identifier);     // "fffh"
+  ExpectedTokens.push_back(AsmToken::EndOfStatement); // "\n"
+  ExpectedTokens.push_back(AsmToken::Eof);
+  lexAndCheckTokens(AsmStr, ExpectedTokens);
+}
 } // end anonymous namespace